I've just completed one complete run-through on this profile and of course it's too long. In several days I will come back and take a couple more run-throughs to cut the length down. Day-1904 19:36, 4 September 2017 (EDT)
I believe all scholars believe a person existed. The debate tends towards his achievements and the fact that Vortigern is also a title (Overlord or High King), thus giving rise to potential duplication. 
Robert Vermaat presents his version of this historical Vortigen. 
Vortigern's Language: Brythonic
During this time period Latin was used as the language of government but a main language of the people was Brythonic and the people were Britons.
The arrival of Saxons and others resulted in the concentration of Brythonic speaking people in western England where it became known as Welsh. The word "Welsh" is generally thought to have an origin in Volcae, a Gallic tribe of the Caesar Julius period, likely pushed out of Gaul into Brittany and then to Britain, displacing the Pictish tribes of origin and pushing them north. When the Saxons arrived they used the term Volca to mean anyone not speaking their language, actually translated it means Roman speaker. In the Saxon language/dialect used in Saxon Britain this would have sounded like walha; thus Welsh.
375 Birth as Vitalinus
He was born in the year 375.  This date estimate would make him aged 35 when the Romans left in 410. He could have married his first wife in 395 at age 20 and his second wife, Severa, daughter of Magnus Maximus, in 405 at age 30.
Italian Wikipedia, as reported by Wikidata, has the dates 394-454
He would have been 74, however, in 449 when Hengest is first said to have come to Britain, and older than that when he married Hengest's daughter Rowena. Day-1904 19:27, 4 September 2017 (EDT)
Vermaat posits that at the end of the Roman era in Britain, there was a man of high standing, whose family had large posessions in the western Midlands, central and south Wales. This man was called Vitalinus and he had acquired a high position in either the British church or in the Civil Service of the Roman Empire. 
Marriage to Severa
Vitalinus was also a rich land-owner, married to a daughter (Sevira) of the late usurper Magnus Maximus. 
We find from the inscription on the shaft of the Cross erected to the memory of his great grandfather, King Eliseg, who died in the year 773, by his great grandson, King Cyngen II, that Vortigern married Scveira, the daughter of the Emperor Maximus, who slew the Emperor Gratian. 
Vortigern was alleged by Peate to have married first an unknown woman who was the mother of all his children except Brydw. 
425 Vitalinus in Power
Vermaat: By the year 425 Vitalinus became the most powerful man in Britain, though he ruled with a Council of representatives (proto-princes) from the Civitates and other emerging centres of regional power. His own power was based largely on the province of Britannia Prima, and a large part of that province later became the kingdom of Powys. 
Vermaat: Even before 425, Vitalinus received troops from Armorica for the defence of Britain and no doubt for his own position. These troops had been serving in the Roman army and were indistinguishable from their Germanic collegues still serving on the continent. The coming of these Germanic forces was later remembered as the Adventus Saxonum, though others arrived at a later date as well. Vortigern, MS from Bologna. c. 1270 
Vitalinus becomes Vortigern
Vermaat: When he became the most powerful ruler in Britain, Vitalinus changed his name to Vortigern for political reasons. 'Vortigern' is no title, but has a distinct political claim through the name, a claim of 'highest ruler among other rulers'. Vortigern then went on to suppress the opposition, as the conflict with Ambrosius at Wallop in 437 shows. Vortigern won that battle. 
It is occasionally suggested by scholars that Vortigern could be a title rather than a personal name. The name in Brittonic literally means "Great King" or "Overlord", composed of the elements *wor- "over-, super" and *tigerno- "king, lord, chief, ruler" (compare Old Breton machtiern, Cornish myghtygern  a type of local ruler - literally "pledge chief")  in medieval Brittany and Cornwall.
However, the element *tigerno- was a regular one in Brittonic personal names (compare St. Kentigern, Catigern, Ritigern, Tigernmaglus, et al.) and, as *wortigernos (or derivatives of it) is not attested as a common noun, there is no reason to suppose that it was used as anything other than a personal name (in fact, an Old Irish cognate of it, Foirtchern was a fairly common personal name in medieval Ireland, further lending credence to the notion that Vortigern was a personal name and not a title).
420-450 Britons Maintain Their Structures
The Britons had some success in maintaining the structures of Roman rule. It is likely that during the years 420 to 450 Vortigern (the Gwrtheyrn of the Welsh tradition) held authority over much of the former Roman province. 
Tradition suggests that he used the Roman method of using one invader against another. Thus, he may have arranged for some of the Votadini or Gododdin (the Brythonic-speaking people living on the banks of the Firth of Fourth) to settle in north-west Wales to resist the incursions of the Irish. 
He allowed Saxons to settle in exchange for their help against the invasions of the Picts. 
441 Revolt of Federates
Vermaat: After some years the federates revolted, for they saw that it was in fact they that held supreme power in Britain due to their military supremacy. 
Vermaat: This revolt happened probably around 441. Vortigern was betrayed and his kingship ended effectively at this point. Whether he disappeared shortly after this, or that his son Vortimer had been king for a brief period is not clear, but I believe he died and Vortimer took over, after which their persons became confused by later authors. 
Vermaat: Was Vortigern responsible for the demise of Britain? With the previous summary in mind, I think not. He acted together with other British rulers at the time, and I do not hold him responsible for the revolt. 
Vermaat: Maybe the British lost at the time of Ambrosius Aurelianus (when we remind ourselves of the continental adventure of Riothamus), or through the civil wars that are mentioned by Gildas. The British had themselves to blame, but Vortigern was an easy scapegoat. 
Vortigen may have been the "superbus tyrannus" said to have invited Hengist and Horsa to aid him in fighting the Picts and the Scots. However, they revolted, killing his son in the process and forming the Kingdom of Kent. It is said that he took refuge in North Wales, and that his grave was in Dyfed or the Llŷn Peninsula. He is cited at the beginning of the genealogy of the early Kings of Powys. 
The Saxons complained of insufficient supplies around 442 and mutinied, this eventually leading to the Battle of Badon in c.500. While Badon was seen as successful the Saxons had built a "Kingdom" around Sussex, Kent, East Anglia, Hampshire and part of Yorkshire. 
449 Arrival of Saxons
Gildas, writing about 100 years after the fact, places the arrival of the Saxons around the year 449. 
Conflict between Britons and Saxons
The BBC historical site treats King Arthur as an historical person.
The great figure in the struggle between the British and the Saxons is Arthur. He may be an inheritor of a Roman tradition, for the Romans had an officer - the Dux Britanniarum (Duke of Britain) - who was leader of a mobile force charged with the duty of protecting the integrity of the Roman province. 
The fact that places commemorating Arthur may be found in widely separated parts of Britain suggests that he held such an office. His greatest victory came in about 496 at Mons Badonicus, a place perhaps in Sussex or possibly near Bath. The victory halted the Saxon advance for at least half a century.
About the year 540, the fatal battle of Cattraeth was fought between the Britons and Saxons, when the former were defeated with such slaughter that, out of 363 British chieftains, three only, of whom one was Aneurin, the son of Caw, Lord of Cwm Cawlyd, escaped with their lives. He was afterwards taken prisoner, loaded with chains, and thrown into a dungeon, from which he
was released by Ceneu, the son of Llywarch H6n. The disastrous battle of Cattraeth caused the migration of numbers of Northern Britons to their kindred race in Wales, and Aneurin is said to have found a refuge at
the famous college of Cattwg in South Wales ; where, about 570, he was treacherously slain by one Eiddin. 
Italian Wikipedia, as reported by Wikidata, has the dates 394-454
His death is estimated as taking place in 459. 
Biography: Vortigern in Legend
The most recent sources question virtually everything believed about Vortigern.
David Peate calls Vortigern an "historical nightmare" who could not have been in all the places and done all the things it is alleged he did. 
A number of legends have developed about Vortigern, particularly as he, representing the Britons, interacted with the Saxons as the Britons lost dominance of England. Sources will be presented here in chronological order to show how the legends developed.
The main source works are
De Excidio et Conquestu Britanniae by Gildas,
a few works by Bede (notably Historia ecclesiastica gentis Anglorum where he mentions him as Vurtigernus and his Chronica Maiora where he appears as Vertigernus,
Hartwaker (the Saxons) von Sachsen Successor. Later sources make Hengist a King of the Saxons before he embarks for England, apparently his eldest son, Harwaker (Hartwake) succeed him in that role. There is no mention of him in any of the early sources and he must definitely be legendary.
Vortigern British leader and legendary son in law of Hengist
540 Gildas Records Britain When the First Saxons Arrived
About 540,  the 6th century historian and monk Gildas provides the first existing record to mention the arrival of the Saxons, writing in De Excidio et Conquestu Britanniae (On the Ruin and Conquest of Britain) which was intended not as history but a sermon condemning the behavior of the Britons. 
Gildas' work is really a sermon and he is particularly derisive regarding the leaders of the Britonic states during the arrival of the Saxons which he covers in Part 2 of his work. The work was written c. 540 although modern scholars now believe it earlier, varying between 490 (which I find unlikely as it predates Badon where he clearly states he wasn't born yet) to 530ish (which I find more likely). Thus he was contemporary. 
There is no doubt Gildas came from Scotland, probably from royalty which would have been Irish/Gaelic at the time, and likely of the Ionian church. He was particularly critical of the church in England at the time (which he covers in part 3 of his work). 
Salient features of Gildas' account are these:
The Saxons were invited as the result of a decision by counsillors and an unnamed "proud usurpur" (superbo tyranno). In Chapter 23, Gildas tells how "all the councillors, together with that proud usurper" [omnes consiliarii una cum superbo tyranno] made the mistake of inviting "the fierce and impious Saxons" to settle in Britain. 
The Saxons were invited to protect the British against the Picts and the Scots, and arrived in three ships of war, "like wolves into the sheep-fold."
It is not clear whether Gildas used the name Vortigern. Most editions published presently omit the name. Two manuscripts name him: MS. A (Avranches MS 162, 12th century), refers to Uortigerno; and Mommsen's MS. X (Cambridge University Library MS. Ff. I.27) (13th century) calls him Gurthigerno. Gildas adds several small details that suggest either he or his source received at least part of the story from the Anglo-Saxons. The first is when he describes the size of the initial party of Saxons, he states that they came in three cyulis (or "keels"), "as they call ships of war". This may be the earliest recovered word of English. 
The Saxons received monthly allotments. Small numbers of Saxons came at first and over time the number became uncontrollably large. When the Britons could not longer pay the allotments, The Saxons broke their treaty and plundered the lands of the Romano-British. 
Gildas also does not consider Vortigern as bad; he just qualifies him as "unlucky" (infaustus) and lacking judgement, which is understandable, as these mercenaries proved to be faithless. 
Gildas repeats a prophecy that the visiting Saxons were "foretold by a certain soothsayer among them, that they should occupy the country to which they were sailing three hundred years, and half of that time, a hundred and fifty years, should plunder and despoil the same." Both of these details are unlikely to have been invented by a Roman or Celtic source. 
Gildas provides that the "Britons" had five "rulers" which he names as:
Constantine of Dumnonia (south west England today, about half of the later Kingdom of Wessex (capital Exeter), Constantine was the "High King",
- Aurelius Conanus, but he doesn't say which part he rules but is particularly vociferous regarding his character. He may not have been the ruler. Gildas names him as the "lion's whelp" suggesting he was the son of the "lion". Gildas used the Book of Revelation, 13-2: the lion, leopard, bear, and dragon to name the rulers.
Vortiporius, King of Dyfed, south west Wales.
Cuneglasus, central and north east Wales
Maelgwn Gwynedd, King of Gwynedd, north west Wales. 
Of note to his work and evidenced here is that these "Kings" are all the "Welsh" kings or at least West country Kings. The Saxons would later break these apart by separating Dumnonia from Wales. None of the other English/Scottish Kingdoms come in for the same treatment and he lauds praise on a person named Ambrosius Aurelianus. 
Gildas also mentions the Battle of Badon (Latin: Mons Badonicus) but, unfortunately, doesn't mention who led the Britons. 
Gildas clearly states that these events occurred prior to the treaty being broken in 442. (If Gildas is correct and Vortigern did allocate land it must be presumed he was a noble of East Briton, not west, and that he flourished c. 420.) 
731 Bede: First to Name Hengist and Horsa
In about 731, Bede wrote the Ecclesiastical History of the English People. Both Gildas and Bede wrote on behalf of the church and provide us our modern day view of Saxons as "the pagan Anglo-Saxons as God's scourge against the reprobate Britons" although Bede suggests opportunity where he provides "any rough treatment was necessary, and ordained by God, because the Britons had lost God's favour, and incurred his wrath" 
Bede's account of this period adds elements not found in Gildas:
Bede gives a date to the Saxon arrival: Bede also supplies the date, AD 449, which was traditionally accepted but has been considered suspect since the late 20th century: "Marcian being made emperor with Valentinian, and the forty-sixth from Augustus, ruled the empire seven years." Michael Jones notes that there are several adventus dates in Bede. In H.E. 1.15 the adventus occurs within the period 449–55; in 1.23 and 5.23 another date, c. 446, is given; in 2.14 the same event is dated 446 or 447. 
The first commanders are said to have been the two brothers Hengist and Horsa"(Duces fuisse perhibentur eorum primi duo fratres Hengist et Horsa). However in a later section of the same work, Bede writes that Hengest was accompanied by his son Oesc when he initially arrived.
Hengist and Horsa, brothers, were the Saxon chieftains. Bede also gives names in the Historia to the leaders of the Saxons, Hengest and Horsa, specifically identifying their tribes as the Saxons, Angles and Jutes (H.E., 1.14,15). 
Bede names Vortigern. The Saxons were invited to Britain by Vortigern, named as King of the Britons, in 449. Bede, writing in the early- to mid-8th century, mostly paraphrases Gildas in his Historia Ecclesiastica Gentis Anglorum and De Temporum Ratione, adding several details, perhaps most importantly the name of this "proud tyrant", whom he first calls Vertigernus (in his Chronica Maiora) and later Vurtigernus (in his Historia Ecclesiastica Gentis Anglorum). The Vertigernus form may reflect an earlier Celtic source or a lost version of Gildas. 
Bede mentions their arrival in three longboats. 
According to early sources Hengist and Horsa arrived in Britain at Ebbsfleet on the Isle of Thanet. 
For a time they served as mercenaries for Vortigern, King of the Britons, but later they turned against him (British accounts have them betraying him in the Night of the Long Knives). Horsa was killed fighting the Britons, but Hengist successfully conquered Kent, becoming the first Anglo-Saxon King of Kent and the forefather of its kings.
Hengist became first Anglo-Saxon King of Kent.
Hengist has a named father and son.
Bede dates the Battle of Badon to 44 years after the Saxon invasion or c. 495. This is generally associated with the Arthur legend and many suggest that Ambrosius Aurelianus was Arthur of legend. 
830 Nennius: Historia Brittonum
The Historia Brittonum (History of the Britons)—until recently attributed to a Nennius, a monk from Bangor, in Gwynedd in Wales—was probably compiled during the early 9th century. The writer mentions a great number of sources. "Nennius" wrote more negatively of Vortigern, who is accused of incest (a possible or perhaps intentional mistake of Vortigern for Vortipor, accused by Gildas of the same crime), oath-breaking, treason, love for a pagan woman, and lesser vices such as pride. 
The Historia Brittonum recounts many details about Vortigern and his sons. *Chapters 31–49 tell how Vortigern (Guorthigirn) deals with the Saxons and Saint Germanus of Auxerre; 
Chapter 56 tells us about King Arthur and his battles; 
Chapters 57–65 mention English genealogies, mingled with English and Welsh history; 
Chapter 66 gives important chronological calculations, mostly on Vortigern and the Adventus Saxonum. 
Excluding what is taken from Gildas, there are six groupings of traditions:
Material quoted from a Life of Saint Germanus. 
These excerpts describe Saint Germanus' incident with one Benlli, an inhospitable host seemingly unrelated to Vortigern, who comes to an untimely end, but his servant, who provides hospitality, is made the progenitor of kings of Powys;
Vortigern's son by his own daughter, whom Germanus in the end raises;
and Vortigern's own end caused by fire brought from heaven by Germanus' prayers.
Comparing this material with Constantius of Lyon's Life of St. Germanus of Auxerre, it suggests that the two are not the same person. It has been suggested that the saint mentioned here may be no more than a local saint or a tale that had to explain all the holy places dedicated to a St. Germanus or a 'Garmon', who may have been a Powys saint or even a bishop from the Isle of Man about the time of writing the Historia Britonum. 
The story seems only to be explained as a slur against the rival dynasty of Powys, suggesting they did not descend from Vortigern, but from a mere slave.
Stories that explain why Vortigern granted land in Britain to the Saxons — first to Thanet, in exchange for service as foederati troops; then to the rest of Kent, in exchange for marriage to Hengest's daughter; then to Essex and Sussex, after a banquet where the Saxons treacherously slew all of the leaders of the British but saved Vortigern to extract this ransom. This is no more than an explanatory legend. No finds suggest the origin of Anglo-Saxon occupation in Thanet or Kent; Dorchester-on-Thames (Oxford) is a more likely candidate,[why?] as is East Anglia.[why?]
The magical tale of Ambrosius Aurelianus and the two dragons found beneath Dinas Emrys. This origin of the later legend of Merlin is clearly a local tale that had attracted the names of Vortigern and Ambrosius to usurp the roles of earlier characters. While neither of them has any association with that remote part of Wales, the character Vortigern is best known to us because of this tale.
A number of calculations attempting to fix the year Vortigern invited the Saxons into Britain. These are several calculations made by the writer, naming interesting names and calculating their dates, making several mistakes in the process.
Genealogical material about Vortigern's ancestry, the names of his four sons (Vortimer, Pascent, Catigern, Faustus), a father (Vitalis), a grandfather (Vitalinus) and a great-grandfather who is probably just an eponym (Gloui) which associates Vortigern with Glevum, the civitas of Gloucester.
The Historia Brittonum relates four battles occurring in Kent, apparently related to material in the Anglo-Saxon Chronicle (see below). In the Historia Brittonum it is claimed that Vortigern's son Vortimer commanded the Britons against Hengest's Saxons. Moreover, it is claimed that the Saxons were driven out of Britain, only to return at Vortigern's re-invitation a few years later, after the death of Vortimer.
The stories preserved in the Historia Brittonum reveal an attempt by one or more anonymous British scholars to provide more detail to this story, while struggling to accommodate the facts of the British tradition. This is important, as it indicates that either at the time, or near that time, there were one or more Welsh kings who traced their genealogy back to Vortigern.
In the work by Ninnius (Historia Brittonum, Chapter 31) we are told that Vortigern and Ambrosius Aurelianus are contemporary and that Vortigern ruled in fear of Ambrosius Aurelianus. Modern scholars suggest that the text suggests that Vortigern feared him more than the Picts. As Chapter 31 precedes the intervention by the Saxons we can assume that Vortigern was more concerned with his war against the other Briton Kingdoms than against the Picts. In Chapter 31 and again in 41 Ambrosius Aurelianus is still regarded as a young man. His origin is unknown, obscure even, but Geoffrey of Monmouth suggests, under the name Aurelius Ambrosius, that he was one of three sons of Constantine III, thus a brother to younger Constans above. But if this so in c 420 then Aurelius Ambrosius would have been an old man indeed at Badon in 495.
Nennius' work is dated variously in the 8th or 9th centuries; an estimated date of 830 places it roughly in time. His work, Historia Brittonum, gives this account: "In the meantime, three vessels, exiled from Germany, arrived in Britain. They were commanded by Horsa and Hengist, brothers, and sons of Wihtgils. Wihtgils was the son of Witta; Witta of Wecta; Wecta of Woden; Woden of Frithowald; Frithowald of Frithuwulf; Frithuwulf of Finn; Finn of Godwulf; Godwulf of Geat, who, as they say, was the son of a god, not of the omnipotent God and our Lord Jesus Christ (who before the beginning of the world, was with the Father and the Holy Spirit, co-eternal and of the same substance, and who, in compassion to human nature, disdained not to assume the form of a servant), but the offspring of one of their idols, and whom, blinded by some demon, they worshipped according to the custom of the heathen. Vortigern received them as friends, and delivered up to them the island which is in their language called Thanet, and, by the Britons, Ruym. Gratianus AEquantius at that time reigned in Rome. The Saxons were received by Vortigern four hundred and forty-seven years after the passion of Christ, and, according to the tradition of our ancestors, from the period of their first arrival in Britain, to the first year of the reign of king Edmund, five hundred and forty-two years; and to that in which we now write, which is the fifth of his reign, five hundred and forty-seven years." 
Nennius thus gives the following additions to the Hengist story.
Exile. Hengist and Horsa and their three vessels were exiled from Germany,
Isle of Thanet. In 447 AD, Vortigern received Hengist and Horsa "as friends" and gave to the brothers the Isle of Thanet. (p. 18 )After the Saxons had lived on Thanet for "some time" Vortigern promised them supplies of clothing and other provisions on condition that they assist him in fighting the enemies of his country. As the Saxons increased in number the Britons became unable to keep their agreement, and so told them their assistance was no longer needed and they should go home. (p. 22) 
Rowena. Hengist had a beautiful daughter, who arrived in a group of 16 vessels, and so bewitched Vortigern that he exchanged Kent for her. Vortigern allowed Hengist to send for more of his countrymen to come over to fight for him. Messengers were sent to "Scythia", where "a number" of warriors were selected, and, with sixteen ships, the messengers returned. With the men came Hengist's beautiful daughter. Hengist prepared a feast, inviting Vortigern, Vortigern's officers, and Ceretic, his translator. Prior to the feast, Hengist enjoined his daughter to serve the guests plenty of wine and ale so that they would become drunk. At the feast Vortigern became enamored with her and promised Hengist whatever he liked in exchange for her betrothal. Hengist, having "consulted with the Elders who attended him of the Angle race," demanded Kent. Without the knowledge of the then-ruler of Kent, Vortigern agreed. (p. 22-23).  Hengist's daughter was given to Vortigern, who slept with her and deeply loved her. Hengist told him that he would now be both his father and adviser and that he would know no defeat with his counsel, "for the people of my country are strong, warlike, and robust." 
Ancestry. Nennius gives an ancestry to Horsa and Hengist, stating that they were brothers, "the sons of Guictglis, the sons of Guigta, the sons of Guectha, and Hengest, the children of Frealaf, and sons of the son of Finn, the son of Wihtgils, the son of Geta, who was, as they say, the Son of God."  The narrative then gives a genealogy of the two: Hengist and Horsa were sons of Guictglis, son of Guicta, son of Guechta, son of Vouden, son of Frealof, son of Fredulf, son of Finn, son of Foleguald, son of Geta. Geta was said to be the son of a god, yet "not of the omnipotent God and our Lord Jesus Christ," but rather "the offspring of one of their idols, and whom, blinded by some demon, they worshipped according to the custom of the heathen." 
With Vortigern's approval, Hengist would send for his son and his brother to fight against the Scots and those who dwelt near the wall. Vortigern agreed and Ochta and Ebissa arrived with 40 ships, sailed around the land of the Picts, conquered "many regions," and assaulted the Orkney Islands.  Hengist continued to send for more ships from his country, so that some islands where his people had previously dwelt are now free of inhabitants. (p. 23-24). 
Vortigern married his own daughter and had a son by her, incurring the wrath of Germanus, Bishop of Auxerre ) and thereupon going into hiding at the advice of his counsel. 
Vortigern turned on the Saxons and attacked them. Vortigern's son Vortimer engaged Hengist and Horsa and their men in battle, drove them back to Thanet and there enclosed them and beset them on the western flank. The war waxed and waned; the Saxons repeatedly gained ground and were repeatedly driven back.. (p. 29)  Vortimer attacked the Saxons four times: first enclosing the Saxons in Thanet, secondly fighting at the river Derwent, the third time at Epsford, where both Horsa and Vortigern's son Catigern died, and lastly "near the stone on the shore of the Gallic sea," where the Saxons were defeated and fled to their ships.
The Feast of Long Knives. After a "short interval" Vortimer died and the Saxons became established, "assisted by foreign pagans." Hengist convened his forces and sent to Vortigern an offer of peace. Vortigern accepted, and Hengist prepared a feast to bring together the British and Saxon leaders. (p. 30-31)  However, he instructed his men to conceal knives beneath their feet. At the right moment, Hengist shouted nima der sexa (get your knives) and his men massacred the unsuspecting Britons. However, they spared Vortigern, who ransomed himself by giving the Saxons Essex, Sussex, Middlesex, and other unnamed districts.(p. 31-32). 
Germanus of Auxerre as British leader. Germanus of Auxerre was acclaimed as commander of the British forces. By praying, singing hallelujah and crying to God, the Saxons were driven to the sea. Germanus then prayed for three days and nights at Vortigern's castle and fire fell from heaven and engulfed the castle. 
Vortigern, Hengist's daughter, Vortigern's other wives, and all other inhabitants burned to death. Potential alternate fates for Vortigern are provided.(p. 33)  However, the Saxons continued to increase in numbers, and after Hengist died his son Ochta succeeded him.(p. 34) 
Conflict between Romans and Britons. "31. After the above-said war between the Britons and Romans, the assassination of their rulers, and the victory of Maximus, who slew Gratian, and the termination of the Roman power in Britain, they were in alarm forty years. Vortigern then reigned in Britain. In his time, the natives had cause of dread, not only from the inroads of the Scots and Picts, but also from the Romans, and their apprehensions of Ambrosius."
Nennius states "This is the genealogy of Vortigern, which goes back to
Fernvail, who reigned in the kingdom of Guorthegirnaim, and was the son of #Teudor; Teudor was the son of
Pascent; Pascent of
Guoidcant; Guoidcant of
Moriud; Moriud of
Eltat; Eltate of
Eldoc; Eldoc of
Paul; Paul of
Meuprit; Meuprit of
Braciat; Braciat of
Pascent; Pascent of
Guorthegirn; Guorthegirn of
Guortheneu; Guortheneu of
Guitaul; Guitaul of
Guitolion; Guitolion of
Gloui. Bonus, Paul, Mauron, Guotelin, were four brothers, who built Gloiuda, a great city upon the banks of the river Severn, and in British is called Cair Gloui, in Saxon, Gloucester. Enough has been said of Vortigern."
In this text Vortigern is given as "Guorthigirn Guortheneu, filii Guitaul, filii Guitolin, filii Glovi" in the original text. Obviously some ancestor that wanted to tell a good story. Why tell it this way? Glovi or Glouvi or Gloiu or Glou is said to have built Cair Glovi (later Gloucester). He is sometimes suggested to be Claudius Caesar (d. 54 AD) and Gloucester is said to have had the first Roman Christian church in Britain (the site is under the St Mary de Lode Church, Gloucester, and was destroyed by the Saxons, rebuilt, destroyed again, likely by Vikings and then built by the Normans). 
Is it possible that Vortigern was a descendent of Claudius? It is, although the name in Roman would have been spelt Clevum (but this is in the wash), and it would certainly have given him the ability to usurp the reign of the Constantine dynasty in Britain. Against it though we are missing a few generations. There are only 2 people named between "Claudius" and Vortigern although Claudius died in 54. Even if Vortigern was born in 375 this means 320 years between them.
Another point to note: In the original text we see "Fernmail ipse est, qui regit modo in regionibus duabus Buelt et Guorthigirniaun, filius Teudubir. Teudubir ipse est rex Bueltiae regionis, filius Pascent, filii Guoidcant, filii Moriud, filii Eldat, filii Eldoc, filii Paul, filii Mepurit, filii Briacat, filii Pascent, filii Guorthigirn Guortheneu, filii Guitaul, filii Guitolin, filii Glovi. Bonus, Paul, Mauron tres fratres fuerunt filii Glovi, qui aedificavit urbem magnam super ripam fluminis Sabrinae, quae vocatur Brittannico sermone Cair Glovi, Saxonice autem Gloecester. satis dictum est de Guorthigirno et de genere suo."
The relevant extract being: "filii Briacat, filii Pascent, filii Guorthigirn Guortheneu, filii Guitaul, filii Guitolin, " This states that Pascent was a son of Vortigern, as we have it on wikitree. 
What about the other way. The passage in the work is clearly not a lineage of Vortigern but that of Fernvail "who reigned in the kingdom of Guorthegirnaim".
Nennius is thought to have lived in Powys, actually spending time in what is now Breckonshire (then much of Guorthegirnaim). Is it likely that Fernvail was his Overlord? Yes? Nennius has been often criticised for exactly this and his work is regarded as questionable. We know Nennius wasn't the only author but really an editor and they often try to associate the "Britons" with the early Celtic and Romano British people, we would likely call it Nationalism today. 
So what about Fernvail. Much of the stuff on the web seems to be rubbish (even having the genealogy in the reverse order) but it seems he may have been born or flourished c. 750/800 and is often regarded as the last king of Guorthegirnaim. After 800 the lands become part of the kingdom of Seisyllwg and then the kingdom of Deheubarth. 
From a number of accounts it appears that Ambrosius Aurelianus, after the death of Voltigern, granted the Kingdom to Pascent / Pasgen ap Gwrtheyrn (3rd son of Vortigern). It seems that Pascent had already been granted Builth and Gwrtheyrnion by his father and this was an agreement by Ambrosius Aurelianus, who was clearly King of Britons at that time (c. 440/450). Geoffrey of Monmouth tells a different story suggesting Ambrosius Aurelianus and Pascent fought their entire lives but I can reconcile the argument. It seems clear that, with Vortigern dead, there was a need to restore what was a significant power base in Wales in his defence of Celtic Britain against the Saxons. There was no point fighting a war on two fronts.
The lineage prior to Vortigern, as given by Ninnius, is extremely questionable. 
Ninnius has a passage which suggests that Vortigern was on the run from St Germanus, sometimes thought to be Germanus of Auxerre. It came about around 447. This visit by Germanus of Auxerre is questioned by historians, and he must have been over 70 at the time, but, I think, his prodigy Germanus of Normandy might have been there and is a better candidate for the story. 
Regardless, the history suggests that Vortigern fled from Germanus after trying to get his daughter to name Germanus as father to her child. Vortigern was cursed by Germanus and the council of Britons, and fled into Wales followed by Germanus and the clergy. 
He is said to have fled to Caer Guorthegirn (Fortress of Vortigern) which is above the river Wye. Nennius describes it as being located in the region of Gueneri or Guenessi. 
According to Ninnius, and the placement of the passage in the text - immediately after the lineage, suggests this is where he died, "fire fell from heaven consuming the castle, the guilty king, and his company" (according to the History of the Welsh Church). 
850 Pillar of Eliseg
The inscription on the Pillar of Eliseg, a mid-9th century stone cross in North Wales, gives the Old Welsh spelling of Vortigern: Guarthi[gern] (the inscription is now damaged and the final letters of the name are missing), believed to be the same person as Gildas' "superbus tyrannus", Vortigern. The pillar also states that he was married to Sevira, the daughter of Magnus Maximus, and gave a line of descent leading to the royal family of Powys, who erected the cross.
870 Anglo-Saxon Chronicle, late 9th Century
Because the date of the material comprising the Historia Brittonum is disputed, and could be later than the Chronicle, some historians argue that the Historia Brittonum took its material from a source close to the Chronicle; but one has to wonder if both do not draw upon an earlier tradition.
These dates post date the mutiny. The Chronicles provide greater detail: they landed in Kent and fought the Picts "defeating them wherever they fought them" - this suggests the Picts had invaded as far as Kent; Hengist and Horsa described "the worthlessness of the Britons, and the richness of the land" and called for more support; more arrived "the three powers of Germany; the Old Saxons, the Angles, and the Jutes"; the Saxons populated Essex, Sussex, and Wessex; the Jutes Kent, the Isle of Wight, and part of Hampshire; and the Angles East Anglia, Mercia, and Northumbria which suggests they followed the Picts all the way north to the then Kingdoms of Bernicia and Deria. Ida of Bernicia and Aella of Diera seem to have been the first Saxon Kings. The time of their appearance on record is later than Badon but it might be expected that the Kingdom wasn't formed until after. 
The Anglo-Saxon Chronicle was created in the late 9th century during the reign of Alfred the Great,  so date it, say, 870. Because the Anglo-Saxon Chronicle originated in monks' attempts to predict the date of Easter, it is arranged by year with notes as to what happened in that year. Therefore it's distinguishing mark, beyond adding new material to the Hengist and Horsa story, is the use of dates.
449 Hengist and Horsa were invited to Britain by Vortigern, landing at Eopwinesfleot (Ebbsfleet). Hengist and Horsa wrote home describing "the worthlessness of the Britons, and the richness of the land" and asked for assistance. Their request was granted and support arrived. Afterward, more people arrived in Britain from "the three powers of Germany; the Old Saxons, the Angles, and the Jutes". The Saxons populated Essex, Sussex, and Wessex; the Jutes Kent, the Isle of Wight, and part of Hampshire; and the Angles East Anglia, Mercia, and Northumbria (leaving their original homeland, Angeln, deserted). Hengist and Horsa, leaders of the forces, were sons of Wihtgils, son of Witta, son of Wecta, son of Woden.
455 Hengist and Horsa fought with Vortigern at Aylesford and that Horsa died there. Hengist took control of the kingdom with his son Esc. 
457, Hengist and Esc fought against British forces in Crayford "and there slew four thousand men". The Britons left the land of Kent and fled to London. 
465, Hengest and Esc fought again at the Battle of Wippedesfleot, probably near Ebbsfleet, and slew twelve British leaders. 
473, the final entry in the Chronicle mentioning Hengist or Horsa, Hengist and Esc are recorded as having taken "immense booty" and the Britons having "fled from the English like fire".
The Anglo-Saxon Chronicle provides dates and locations of four battles that Hengest and his brother Horsa fought against the British in southeast Britain in the historic county of Kent. 
Vortigern is said to have been the commander of the British for only the first battle; the opponents in the next three battles are variously termed "British" and "Welsh", which is not unusual for this part of the Chronicle. 
No Saxon defeat is acknowledged, but the geographical sequence of the battles suggests a Saxon retreat, and the Chronicle locates the third battle, dated 465 in Wippedsfleot, as the place where the Saxons first landed, thought to be Ebbsfleet near Ramsgate. 
The Anglo-Saxon Chronicle presents the year 455 as the last date when Vortigern is mentioned. 
However, the Chronicle is not a single document but the end result of combining several sources over a period of time. The annals for the 5th century in the Chronicle were put into their current form during the 9th century, probably during the reign of Alfred the Great. 
The sources for the fifth century annals are obscure, however an analysis of the text demonstrates some poetic conventions, so it is probable that they were derived from an oral tradition, such as sagas in the form of epic poems.
Vortigern doesn't re-appear after 455. The Battle of Aylesford is key to the study. 
The Anglo Saxon chronicles clearly state with while the Historia Brittonum (by Nennius) suggests the battle was fought against Vortimer and Catigern (sons of Vortigern) who had risen up against the rule. This may have been a result of marrying his pagan wife, Rowen. Historia Regum Britanniae, Book VI, chapter 13, alludes to this. 
The Anglo Saxon Chronicles rarely discuss opponents and it might be that the Battle of Aylesford was an attempt to usurp their father. In either event Vortigern was likely dead before or around this event. If we assume these dates d. c 455 then he must have been old for the day (if born c. 375) and it seems highly improbable that he fought at Aylesford.
1100 William of Malmesbury
Writing prior to Geoffrey of Monmouth, William of Malmesbury was noted for adding to the damnatio memoriae of Vortigern: At this time Vortigern was King of Britain; a man calculated neither for the field nor the council, but wholly given up to the lusts of the flesh, the slave of every vice: a character of insatiable avarice, ungovernable pride, and polluted by his lusts. To complete the picture, he had defiled his own daughter, who was lured to the participation of such a crime by the hope of sharing his kingdom, and she had borne him a son. Regardless of his treasures at this dreadful juncture, and wasting the resources of the kingdom in riotous living, he was awake only to the blandishments of abandoned women. — Gesta Regum Anglorum 
No other sources confirm this evil description, and it seems safe to assume that this is an exaggeration of accusations made by earlier writers. William does, however, add some detail, no doubt because of a good local knowledge. In De Gestis Regum Anglorum book I, chapter 23.
1150 Geoffrey of Monmouth, History of the Kings of Britain, 12th century
Geoffrey of Montmouth, in his History of the Kings of Britain, gives the most detailed accounts of Hengist and Horsa, including the elements described earlier, and adding the following:
Vortigern did not invite Hengist, but when three brigandines or long galleys arrived in Kent, full of armed men and commanded by the two brothers, Vortigern who was then staying at Dorobernia (Canterbury), ordered that the "tall strangers" be received peacefully and brought to him. When Vortigern saw the company, he immediately observed that the brothers "excelled all the rest both in nobility and in gracefulness of person." He asked what country they had come from and why they had come to his kingdom. Hengist ("whose years and wisdom entitled him to precedence") replied that they had left their homeland of Saxony to offer their services to Vortigern or some other prince, as part of a Saxon custom in which, when the country became overpopulated, able young men were chosen by lot to seek their fortunes in other lands. Hengist and Horsa were made generals over the exiles, as befitted their noble birth, and then assisted Vortigern with his wars, receiving rewards in return.
Hengist received repeated approvals for requests to bring more warriors from Germany to assist in Vortigern's wars. He was given approval to build a castle on a piece of land small enough that it could be encircled by a leather thong. Vortigern granted this and ordered Hengist to invite more Saxons. After executing Vortigern's orders, Hengist took a bull's hide and made it into a single thong, which he used to encircle a carefully-chosen rocky place (perhaps at Caistor in Lindsey).  Here he built the castle of Kaercorrei, or in Saxon Thancastre: "thong castle."
Vortigern met Hengist's beautiful daughter, now named Rowena, when she arrived from Germany with eighteen ships full of the best soldiers possible. Hengist invited Vortigern to a celebratory banquet at which Vortigern asked to marry Rowena and granted Hengist Kent in return.  (p. 120-121)
Vortigern's marriage to Rowena incurred the hatred of his nobles and his three sons.  (p. 121)
Hengist used his status as father-in-law to claim an advisory role with Vortigern, and to obtain lands in the northern parts of Britain for his sons Octa and Ebissa.  (p. 121-122)
As Vortigern allowed more and more Saxons to enter, the Britons turned against him and took his son Vortimer for their king. In a series of battles Horsa and Vortimer's brother Catigern were killed and the defeated Saxons fled to Thanet and then boarded their ships and left, leaving their wives and children behind. (p. 122-123)
Rowena, however, poisoned the victorious Vortimer and Vortigern returned to the throne. (p. 123)
Vortimer invited Hengist back to Britain, instructing him to bring only a small retinue. Hengist instead raised an army of 300,000 men. When Vortigern caught word of the imminent arrival of the vast Saxon fleet, he resolved to fight them. Rowena alerted her father of this, who, after considering various strategies, resolved to make a show of peace and sent ambassadors to Vortigern. (p. 124-125)
At a banquet later known as the "night of the long knives", Vortigern and his men arrived to make peace, but were slain by Hengist's men who had hidden their long daggers beneath their clothing. Vortigern was spared and ransomed himself by relinquishing more British territory, including Britain's chief cities, to the Saxons. Once free, Vortigern fled to Cambria (Wales). (p. 125-126)
In Cambria, Merlin prophesied to Vortigern that the brothers Aurelius Ambrosius and Uther Pendragon, who had fled to Armorica as children after Vortigern killed their brother and father, would return to have their revenge and defeat the Saxons. They arrived the next day, and, after rallying the dispersed Britons, Aurelius was proclaimed king. Aurelius marched into Cambria and burned Vortigern alive in his tower, before setting his sights upon the Saxons.  (p. 149)
Hengist was struck by terror at the news of Vortigern's death and fled with his army beyond the Humber. He took courage at the approach of Aurelius and selected the bravest among his men to defend. Hengist told these chosen men not to be afraid of Aurelius, for he had brought less than 10,000 Armorican Britons, while there were 200,000 Saxons. Hengist and his men advanced towards Aurelius in a field called Maisbeli (probably Ballifield, near Sheffield),
intending to take the Britons by surprise, but Aurelius anticipated them.Cite error 2; Invalid <ref> tag; refs with no content must have a name (p. 149)
As they marched to meet the Saxons, Eldol, Duke of Gloucester told Aurelius that he greatly wished to meet Hengist in combat, noting that "one of the two of us should die before we parted." He explained that he had been at the Treachery of the Long Knives, but had escaped when God threw him a stake to defend himself with, making him the only Briton present to survive. Meanwhile, Hengist was placing his troops into formation, giving directions, and walking through the lines of troops, "the more to spirit them up."  (p. 150-151) A furious battle commenced. The Saxons maintained their ground despite heavy losses. Then a detachment of horses from the Armorican Britons arrived led by Gorlois, Duke of Cornwall arrived, and Eldol, knowing the day was won and grabbed Hengist's helmet, dragging him into the British ranks. The Saxons fled. Hengist's son Octa retreated to York and his kinsman Eosa to Alclud (Dumbarton). (p. 153)
After a council three days after the battle, Eldol beheaded Hengist. Octa and Eosa surrendered to Aurelius, who granted them the country bordering Scotland and made a firm covenant with them.  (p. 154)
Just after the Romans leave, the archbishop of London is put forward by the representatives of Britain to organise the island's defences. To do so, he arranges for continental soldiers to come to Britain. The name of the bishop is Guitelin, a name similar to the Vitalinus mentioned in the ancestry of Vortigern and to the Vitalinus said to have fought with an Ambrosius at the Battle of Guoloph (Battle of Wallop). This Guithelin/Vitalinus disappears from the story as soon as Vortigern arrives. All these coincidences imply that Geoffrey duplicated the story of the invitation of the Saxons, and that the tale of Guithelinus the archbishop might possibly give some insight into the background of Vortigern before his acquisition of power.
Geoffrey states that Vortigern was the successor of Constans, the son of the usurping emperor Constantinus III. Vortigern used Constans as a puppet king and ruled the nation through him until he finally managed to kill him through the use of insurgent Picts.
Geoffrey is the first to mention Hengest de Cantia Regnum and the name of Hengest's daughter, who seduces Vortigern to marry her, after which his sons rebel, as a certain Ronwen recorded Rowena, also called Renwein, neither of which is a Germanic name. 
Like the Historia Brittonum, Geoffrey adds that Vortigern was succeeded briefly by his son Vortimer, only to assume the throne again when Vortimer is killed.
Geoffrey provides that Vortigern was the Leader of the Gewissei tribe "Dux Gewissei". They were a tribe of Britons based around Dorchester on Thames and it is entirely probable that they held large tracts of lands in Kent. It is not clear whether they existed prior to the Anglo Saxon occupation but they were certainly allied and supported by it, indeed many historians treat Gewisse (which is a Saxon name anyway) and West Saxons and Wessex synonomously.
The Gewissei are known to have fought against the "Britons" notably at Old Sarum in 552 and Barbury Castle in 556. Later, by 680 they held control of Hampshire and later became the founders of the Kingdom of Wessex. If we follow this line and accept Geoffrey of Monmouth the only other time we see the phrase "Dux Gewisse" is when he discusses Octvian, father-in-law to Magnus Maximus who appears in most of the 15 Tribes of Wales. 
Geoffrey of Monmouth states that Maximianus was titled king of the Britons following the death of Eudaf Hen (Lt: Octavius). In Geoffrey's account, Octavius was a half-brother to Constantine I, who, under Roman rule was called King of the Britons following the death of his father Constantius (d. 306). 
Constantine became Roman Emperor leaving Briton to a proconsul. Octavius then rose up and killed the proconsul and, of course, Constantine sent an army to quell the uprising. Although initially fleeing Britain, for Norway, he returns and eventually defeats the Roman legions thus reclaiming the title King of Britons. He eventually abdicates the throne in favour of Maximianus. 
Geoffrey of Monmouth's account suggests that Vortigern was the successor of Constans, the son of the usurping emperor Constantinus III. Further, Vortigern used Constans as a puppet king and ruled the nation through him until he finally managed to kill him through the use of insurgent Picts. 
A valley on the north coast of the Lleyn Peninsula, known as Nant Gwrtheyrn or "Vortigern's Gorge", is named after Vortigern, and until modern times had a small barrow known locally as "Vortigern's Grave", along with a ruin known as "Vortigern's Fort". However, this conflicts with doubtful reports that he died in his castle on the river Teifi in Dyfed ("Nennius") or his tower at Little Doward in Herefordshire (Geoffrey of Monmouth).
Other fortifications associated with Vortigern are at Arfon in Gwynedd, Bradford-on-Avon in Wiltshire, Carn Fadrun in Gwynedd, Clwyd in Powys, Llandysul in Dyfed, Old Carlisle in Cumberland, Old Sarum in Wiltshire, Rhaeadr Gwy in Powys, Snowdon and Stonehenge in Wiltshire. 
1881 Jacob Youde
Writing in 1881, Jacob Youde stated that in 446, Gwetheyr Gwrthened, of Voltiger, Prince of Erging, Ewiaa and Caer Glouyw or Gloucester, was elected King of Britain, upon the assassination of King Conataos in the year 446. 
The Brut of G. ab Arthur states, that Gwrtheyrn Gwrtheneu, Prince of Erging and Ewias, became King of Britain after the assassination of King Constans in 385, Haigh in his IIistoy of the Conquest of Britain by the Saxons, in 425, and the Brut of G. ab Arthur states, that in 430 Uthyr and Emrys or Ambrosius, the sons of Cystennyn Fendigaid, King of Britain, and brothers of the late King Constans, came with a large army against Vortigern, who fled towards Cymru (Wales) and took up his quarters in his castle of Goronwy in Erging, which
was built on the summit of a mountain, called Mynydd Denarcb, on the banks of the river Wye, which river flows from Mynydd KJorach. On their arrival there,
Uthyr and Emrys calling to mind that Vortigern had been the cause of the deaths of their father and brother, and had brought the Saxons into the country, they determined to besiege that castle, and to burn it down to
the ground ; and all that were in the castle, both of men and beasts, were burnt. And Gwrtheyrn was slain and burnt. 
Other accounts state that in 448, Vortigern was compelled by Uthyr and Aurelius Ambrosius (Emrys) to take refuge in his fortress of Caer Gwrtheyrn in Erging, whither he was accompanied by St. Germanus, who is said to have remained with him to the last, imploring him to repent and make his peace with God. Seeing that remonstrance was in vain, Germanus left the King,
and retired to Italy, where he died at Ravenna, 25 July 448. 
From this it appears that two British Kings, Benlli Gawr and Vortigern, both perished with their garrisons in the conflagration of their respective fortresses, in the same year, from not attending to the advice and the remonstrances of Germanus, Bishop of Auxerre. Other accounts, however, state that Vortigern did not perish in the fortress of Castell Goronwy, or Caer Gwrtheyrn, which
last name the fortress may have received in after times, but that he escaped from the conflagration, and died in obscurity at Llanaelhaiarn in Carnarvonshire ; where a tomb, in which the bones of a man of large stature were found, which has always been designated as " Bedd Gwrtheyrn, the grave of Vortigern, and the neighbouring valley has ever since borne the name of Nant Gwrtheyrn. 
One of the names of the traditional burial places of Vortigern is preserved in stanza xl of the collection entitled the " Verses of the Graves," or " Verses of the Warriors", in the Black Book of Caermarihen : — 
" Ebet yn ystyuacheu,
Y mae paup yny amheu,
Bet gurtheyra giirtheneu/^
Four Ancient Books of Wales, ii, 32.
The grave m Ystyvacliau, Which everyone suspects to be The grave of Gwrtheym Gwrtheneu/'
In order to secure himself on the throne of Britain, Gwrtheym invited over the Saxons under Hengist and Horsa in 454. 
And soon afterwards he married Rhonwen or Rowena, the daughter of Hengist, upon whom he bestowed in a drunken fit the Isle of Thanet in Kent. 
In 464, the Britons succeeded in defeating the Saxons, and then made his son Vortimer or Gwrthevyr, called also Gwrthevyr Fendigaid, King instead of Vortigern ; but the former having been poisoned by means of his step-
mother in 468, Vortigern was set upon the throne and reigned till 481, when he was attacked by Emrys and Uthjrr, the sons of Constantine, in his castle of Goronwy- in-Erging on the Wye. 
King Gwrtheym Gwrtheneu left issue by his first wife Seveira (the daughter of the Emperor Flavius Clemens Maximus, a Spaniard, who was Governor of Britain in 370, and having defeated and slain the Emperor Gratian, was proclaimed Emperor of Rome, by the army in Britain, in 383, and who was put to death by Theodosius at Aquileia in 388) 
Gwartimer, one of three sons Vortigern had by his Queen Seveira, who afterwards became King of Britain. 
Cyndeym, one of three sons Vortigern had by his Queen Seveira.  From this second son Cyndeym descended the Kings and Princes of Powys, and the Tribe of Tudor Trevor, but according to the monk Nennius, they descended from a totally different stock.  Kenuius states that during the reign of Yortigcm a certain St. Germanus, Bishop of Auxerre in Gaul, came over to Britain, having been sent there by Pope St. Celestine II to restore Christianity. Amongst others, Germanus went to visit Benlli Gawr, a king whose territories comprised the province Teymllwg. His castle was situate on a hill between Rhuddin and Y Wyddgrilg (Mold), still called after him Moel Fenlli. Thither Germanua went, but the King declining to have anything to do with him, and having ordered him away, a young man named Cadell, one of the King's servants, gave him shelter, which having obtained, the monk Nennius declares that the anger of God fell on the King, and that
" ignis de cjelo cecidit et combussit arcem, et omnes qui cum tyranno erant, nee ultra apparuerunt nee arx resedificatc est, usque in hodiernem diem" ; and that Germanus made Cadell King of Teyrnlhvg, and that he became
the ancestor of the Kings of Powys.  After the death of Benlli Gawr, King of Teymllwg, St. Germanus anointed Cadell, the young man who had entertained him so hospitably, and made him King of
Teymllwg, from which circumstance he received the name of Cadell Deymllwg, and from him Nennius states the Kings of Powys descend. This must have occurred either in 447, or in 448, for in that latter year, Germanus left Britain with the Roman Legions and went to Ravenna, where he died July 25, 448.  Cadell had nine sons when he became King of Teymllwg.  Cyndeyrn bravely fought against the Saxons, and was slain in 457. He was the father of
Rhuddfedyl Frych, the father of Rhydwf, the father of Pasgen, whose name is mentioned in the inscription on the column of Eliseg.
Fasccns, one of three sons Vortigern had by his Queen Seveira, who afterwards became King of Buallt. 
Vortimer, the eldest, who, as we have seen, fought four times against the Saxons, and put them to flight. Gwerthefyr Fendigaid (or Vortimer), who had daughter S. Madrun who may have married Ynyr Gwent I Vortimer Fendigaid born 402 When Vortigern, born 375, would have been aged 27.
Categirn, who was slain in the same battle with Horsa. Cateyrn, had son Rhuddfedel Frych and possible son Cadell Ddrynllug, the latter the King of Powys. 
Pascent, who reigned in the two provinces Builth and Guorthegirnaim, after the death of his father. These were granted him by Ambrosius, who was the great king among the kings of Britain. Pasgen, King of Buellt and Gwrtheyrnion, who had Mawgan and Brincat
daughter, had son Faustus by Vortigern, her father.
The fourth was Faustus, born of an incestuous marriage with his daughter, who was brought up and educated by St. Germanus. He built a large monastery on the banks of the river Renis, called after his name, and which remains to the present period.
Audoacre or Eadwacer, a Saxon leader who fought Childeric, King of the Franks, has been disconnected as there is no reason to believe he was the son of either Vortigern of the Britons (born ca 375 or of Rowena, a legendary daughter of Hengist.
Line of Descent from Magnus Maximus
The following substantially legendary line of descent is mostly derived from Historum Brittainorum, dated 828, so at its earliest it is reporting events 500 years earlier without further documentation. 
Emperor Magnus Maximus (c. 335-388) (? m. Helen)
Severa m. Vortigern, King of Britain (c. 370-c. 441)
Pascent, King of Buellt and Gwrtheyrnion (b. c. 410)
Riagath, King of Buellt and Gwrtheyrnion (b. c. 445)
Mepurit, King of Buellt and Gwrtheyrnion (b. c. 485)
Paul, King of Buellt and Gwrtheyrnion (b. c. 520)
Eldoc, King of Buellt and Gwrtheyrnion (b. c. 555)
Eldad, King of Buellt and Gwrtheyrnion (b. c. 590)
Moriud, King of Buellt and Gwrtheyrnion (b. c. 625)
Guoidcant, King of Buellt and Gwrtheyrnion (b. c. 660)
Pascent, King of Buellt and Gwrtheyrnion (b. c. 700)
Gloud (b. c. 735)
Brawstudd (b. c. 775) m. Arthfael, King of Glywysing (b. c. 765)
↑ Gildas, De Excidio et Conquestu Britanniae, chapter XXIII, text and translation of the quoted passage in Vermaat, Robert. "Gildas and Vortigern". Vortigern Studies. Vortigernstudies.org.uk. Retrieved 2010-01-28. Wikipedia, Vortigern.
↑Hors et Hengist, qui et ipsi fratres erant, filii Guictglis, filii Guigta, filii Guectha, filii VVoden, filii Frealaf, filii Fredulf, filii Finn, filii Fodepald, filii Geta, qui fuit, ut aiunt, filius dei. Ninnius. p. 33 in Rev. J. A. Giles. History of the Ancient Britons. London, George Bell, 186, Fleet Street, 1847. Volume II, Appendix of Original Documents. Accessed September 3, 2017, jhd
↑ 29.029.129.229.329.4 Ingram, James Henry (1823). The Saxon chronicle, with an English Translation and Notes, Critical and Explanatory. London: Longman, Hurst, Rees, Orme, and Brown, Paternoster-Row. Pages 13-16. Cited in Wikipedia. Hengist and Horsa Accessed September 1, 2017. jhd
↑ Swanton, Michael (1998). The Anglo-Saxon Chronicle. New York; London: Routledge. pp. xxi–xxviii. ISBN 0-415-92129-5. Cited by Wikipedia.
↑ Jones, Michael E. (1988). The End of Roman Britain. Ithaca, New York: Cornell University Press. p. 71. ISBN 0-8014-8530-4. Cited by Wikipedia.
↑ Gransden, Antonia (1974). Historical Writing in England c.550-c1307. London: Routledge and Kegan Paull. pp. 36–39. ISBN 0-7100-7476-X. Cited by Wikipedia.
↑ John Sharpe (trans.), The History of the Kings of England and the Modern History of William of Malmsbury, London: W. Bulmer & Co., 1815. Cited by Wikipedia.
↑ 34.0034.0134.0234.0334.0434.0534.0634.0734.0834.0934.1034.11 Thompson, Aaron (1842). The British History of Geoffrey of Monmouth: In Twelve Books. London: James Bohn. Pages 116-155. In his pseudo-historical twelfth century work The History of the Kings of Britain, Geoffrey of Monmouth adapted and greatly expanded the account in the History of the Britons. Hengist and Horsa appear in books 6 and 8. Cited in Wikipedia. Hengist and Horsa Accessed September 1, 2017. jhd
↑ English, Mark (2014). "Maisbeli: A Place-Name Problem from Geoffrey of Monmouth". Notes & Queries. 259: 11–13. Retrieved 14 July 2014. Cited in Wikipedia. Hengist and Horsa Accessed September 1, 2017. jhd
↑ In a discussion on the
Soc.Gen.Medieval List, Isla McDonald displayed a line of descent provided in Peter Bartrum's Welsh Genealogies AD 300-1500 , with dates adjusted by her. The descent in turn came from Historia Brittainorum (828). McDonald said that the first three generations could be deduced from the early accounts of Vortigern's family and the Pillar of Eliseg (9th century). Stewart Baldwin responded that "although Magnus Maximus was historical, and there is no good reason to doubt the existence of Vortigern, Helen is completely fictional, and Severa was probably also an early invention." Accessed Sept 6, 2017. jhd
Lyon, Bryce. "From Hengist and Horsa to Edward of Caernarvon: Recent writing on English history" in Elizabeth Chapin Furber, ed. Changing views on British history: essays on historical writing since 1939 (Harvard University Press, 1966), pp 1–57; historiography
Lyon, Bryce. " Change or Continuity: Writing since 1965 on English History before Edward of Caernarvon," in Richard Schlatter, ed., Recent Views on British History: Essays on Historical Writing since 1966 (Rutgers UP, 1984), pp 1–34, historiography
Thorpe, Benjamin (1855). The Anglo-Saxon Poems of Beowulf, the Scôp or Gleeman's Tale, and The Fight at Finnesburg. Oxford University Press.
'Vortigern,' as it were, is the 25th great-grandfather of Princess Marjorie Bruce Stewart, daughter of Robert I 'The Bruce' King of Scotland, and mother of Robert II Stewart, King of Scotland; and thereby, he (Vortigern) is my 49th great-grandfather by Princess Marjorie.