While the arrivals of Saxons in Britain certainly can presume some first Saxon leader, whether this leader was an actual individual named Hengist is doubtful.
Stewart Baldwin writes, "Rowena never existed. She is an invention of later writers. The existence of Hengist is questionable at best. Of these individuals,
Vortigern is the only one who is clearly historical. There are number of Welsh pedigrees which give claims of descent from Vortigern, but none are contemporary. Since Vortigern was the earliest post-Roman British leader who was mentioned in the early sources, he became a natural ancestor to claim, true or not." 
The Arrival of Saxons in England
A history of the Saxon period presented by BBC states that the Saxons arrived in England after the Roman withdrawal, and adds that "The Anglo-Saxon period lasted for 600 years, from 410 to 1066, and in that time Britain's political landscape underwent many changes." 
Gildas, writing about 100 years later, places the arrival of the Saxons around the year 449. 
Hengist Named in Finnsburg Fragment
Some scholars, notably J. R. R. Tolkien in his work Finn and Hengest, argue that Hengist and his brother Horsa have an historical basis.  This perspective is supported by the appearance of a Hengist in line 34 of the Finnsburg Fragment, which describes the legendary Battle of Finnsburg.  The Finnsburg fragment was a fragment of text found in Lambeth Palace dealing with a conflict occuring between Danes and Frisians as early as the year 400. The lack of any Christian references suggests an early pre-Christian dating for the fragment.  Hengest is mentioned in lines 1082 and 1091. This fragment names only Hengist, however, not Horsa. Tolkein argues that the historical Hengist then came to Britain following the events recorded in the Finnsburg Fragment and Beowulf.  Beyond these statements, no documentation has been found for the historical existence of Hengist.
425 Birth Estimation for the leader of the first Saxon Arrivals
Whether the leader of the first Saxons to arrive was named Hengist or not, since WikiTree profiles require a birth year, estimate that the year of arrival in England was 449 and that the leader was aged, say, 24 or 25. This would place the person's birth at, say, roughly 425. This age is young for an established king, but not unreasonable for a vigorous warrior seeking new territory.
Links to Persons Associated with Hengist
While Tolkein's arguments may support Hengist as the possible name of the first Saxon chieftain in Britain, they do not support the relationships with family members attributed to him, which must be considered legendary. Therefore Hengist's profile is not linked to parents, spouses or children. Links are provided below to other profiles often associated with Hengist:
Hartwaker von Sachsen, born 455. Hengist's Successor. Later sources, for instance Anderson, p. 447, Table CCXV and p. 733, Table CCCCLXXX, 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. Same person probably, as Hatwigate Sachsen and Hartwake (Of Saxony) Sachsen
Osta of Asgard, born 462. Oesc/Aesc (Oisc/Oeric/Oese), sometimes his son, and sometimes his grandson Of the supposed children, most likely a real person.
Vortigern British leader and legendary son in law of Hengist
Was There a Female Hengist?
Some online genealogies list a female Hengist, usually as the wife of Cerdic, the first King of Wessex.  It would also be highly unusual to use the same name for a male and a female. None of ancient sources mention a female Hengist or Hengest, so it may be assumed none exist either in fact or in legend.
Biography: In Legend
540 Gildas: First Saxon Arrivals Invited by Vortigern
About 540,  the 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 mentions the Saxons being invited by Vortigern and his councillors to protect them against the Picts and the Scots, and that the Saxons arrived in three ships of war, "like wolves into the sheep-fold."
Gildas does not, however, name any of the Saxon leaders. As of Gildas' account, the story has these elements:
Saxons invited by Vortigern
Arrival in three ships
731 Bede: First to Name Hengist and Horsa
It is Bede, in the  Ecclesiastical History of the English People, completed in about 731, who states that "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.
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 forefather of its kings.
Bede relates that Horsa was killed in battle against the Britons and was thereafter buried in East Kent, where at the time of writing a monument still stood to him. 
Added to the story of Vortigern's invitation, they are the invitees, whose help Vortigern sought against the Scots and Picts. Turning against the Britons at
some point, Hengist became the first Anglo-Saxon, King of Kent.
According to Bede, Hengist and Horsa were the sons of Wictgils, son of Witta, son of Wecta, son of Woden.  Later in the same work, Bede notes that Hengist was the father of Oeric, and that Oeric accompanied Hengist upon his invitation by Vortigern.
There are no existing records contemporary with these events; the earliest currently available that names Hengist was written about 300 years later. Consequently there is continual discussion over whether Hengist and Horsa, actually existed, and which parts of the story may be factual and which legendary.
Additions to the narrative by Bede:
Hengist and Horsa, brothers, were the Saxon chieftains.
Hengist became first Anglo-Saxon King of Kent.
Hengist has a named father and son.
Before Hengist and Horsa: The Horse Legends
Legends of horse-associated founding brothers are attested among other Germanic peoples, and appear in other Indo-European cultures. As a result, scholars have theorized a pan-Germanic mythological origin for Hengist and Horsa, stemming originally from divine twins found in Proto-Indo-European religion. 
Mallory (2005) notes that the Old English names Hengest [hendʒest] and Horsa [horsɑ] mean "stallion" and "horse" respectively. 
Tolkein adds that that Horsa may be a pet form of a compound name with the first element "horse".
Several sources attest that the Germanic peoples venerated a divine pair of twin brothers. The earliest reference to this practice derives from Timaeus (c. 345 – c. 250 BC). The twins include Castor and Pollus; Raos and Raptos; Ibur and Aio, Aggi and Ebbi. Scholars have theorized that these divine twins in Indo-European cultures stem from divine twins in prehistoric Proto-Indo-European culture. 
Mallory comments on the great importance of the horse in Indo-European religion, as exemplified "most obviously" by various mythical brothers appearing in Indo-European legend, including Hengist and Horsa.
830 Nennius: Historia Brittonum
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 the following additions to the Hengist story.
Hengist and Horsa and their three vessels were exiled from Germany,
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) 
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." 
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) 
870 Anglo-Saxon Chronicle, late 9th Century
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".
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)
Hengist's death is reported for the year 488 at Tunbridge Castle, Kent. 
Legendary Saxon Line of Descent from Witigail to Witikind
George Fisher in 1832 published his Genealogical Companion in which he presented a line of descent of princes and kings in Saxony from Hengist's father Witigail to Witikind the Great, conquered by Charlemagne. While many of these princes exist only in legend, they appear in many popular genealogies and therefore their line of descent is presented here for reference. Birth years are estimated and not part of Fisher's table.
Wihtgils or Witigail, born 380, King of the Saxons, died 434
Dieteric, born 670,, King of the Saxons, died 740, married Dobogesa, daughter of Billung, King of the Vandals
Wernich, born 705, son of Dieteric, King of the Saxons, died 768. Wernich had a brother Ethelbard, also son of Dieteric, also King of the Saxons. Ethelbard had two sons; Albion, was baptized by his cousin Witikund the Great, son of Ethelbard, 785, and Herman was slain by Charlemagne 798,
Witikind the Great, born 755, the last King of the Saxons, conquered by Charlemagne, 785. Consentng to be baptized, the conqueror made him the first Duke of the old Upper Saxony, or on the Weser. He died 807 and was the patriarch of many great families in Europe, amongst whom may be reckoned the present Royal Family of England.
↑ Michael-Hadrill, John Michael (1993). Bede's Ecclesiastical History of the English People: A Historical Commentary. Oxford University Press. ISBN 0-19-822174-6. Page 215. Cited in Wikipedia. Hengist and Horsa Accessed September 1, 2017. jhd
↑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
↑ 24.024.124.224.324.4 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
↑ 25.0025.0125.0225.0325.0425.0525.0625.0725.0825.0925.1025.11 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
↑ Database online. Data: Text: Record for King Hatwigate De Saxony and Record for Hengest DeKent
↑ George Fisher. A Genealogical Companion and Key to the history of England: Consisting of copious genealogical details of the British Sovereigns, Page 25 London: Simkin and Marshall, 1832. Accessed August 3, 2018 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.