William was born before 1200. He was old enough In 1215 to participate, with his father, in the baronial rebellion against King John.
In December 1215 he and his father were excommunicated by Pope Innocent III on 16 Dec 1215, for rebellion against King John.
On 20 May 1217 he was among the rebels captured in the Battle of Lincoln, but secured his release on 26 Oct 1217. He paid 20 marks for his freedom.
He fought in Brittany in 1230, Gascony in 1242 and Wales in 1258.
In 1237 he was one of the barons who escorted Alexander II, King of Scotland to a meeting with Henry III at York which led to a treaty establishing an agreed boundary between Scotland and England.
In 1252 he went on pilgrimage to Santiago da Compostella in Spain.
Marriage and Children
William married Lucy FitzPiers, daughter of Piers (Peter) FitzHerbert, Sheriff of Yorkshire, Keeper of Pickering Castle and Alice FitzRoger, before 24 January 1234. William and Lucy had six sons and two daughters:
Sir William de Roos died in 1257/8 or 1264. He was buried at Kirkham Abbey, Yorkshire.
Possible Daughter Anne
One source raises just a possibility of a daughter Anne not listed elsewhere. The Visitations of the County of Nottingham include a Sutton pedigree which shows "Serius Lord Sutton of Sutton in Holdernese 3d of that name" married to "Anne d. of Willm. Lord Rosse." No dates are given, and the Visitation pedigree conflicts with another Sutton pedigree in Charles Frost's "Notices relative to the early history of the town and port of Hull". This does not show any Serius (or Saerus) Sutton married to a daughter of William Rosse.
Another daughter, Dorothea, has formerly been attached to William de Ros, with no indication of the mother. She is not listed in Douglas Richardson. As of 9 June 2019, her profile was orphaned and the only sources on it are an imported GEDCOM and Ancestry family trees. She has now been detached.
↑ Charles Frost. "Notices relative to the early history of the town and port of Hull", pub. J B Nichols, London, 1827, pedigree facing p. 99, Internet Archive and Google Books
Richardson, Douglas. Magna Carta Ancestry: A Study in Colonial and Medieval Families, 4 vols, ed. Kimball G. Everingham. 2nd edition. Salt Lake City: the author, 2011. See also WikiTree's source page for Magna Carta Ancestry.
Richardson, Douglas. Royal Ancestry: A Study in Colonial and Medieval Families, 5 vols, ed. Kimball G. Everingham. Salt Lake City: the author, 2013. See also WikiTree's source page for Royal Ancestry.
Cokayne. G E. Complete Peerage, New Edition, volume XI, St Catherine Press, 1949
Weis, Frederick Lewis, with additions by Walter Lee Sheppard with William R Beall. The Magna Carta Sureties, 1215, Genealogical Publishing Company, fifth edition, 1999, p. 152, line 116.2
As a holding operation, I have added a research note on the suggestion that there was a further daughter, Anne. The evidence for her existence as a daughter of the William of this profile looks fairly thin to me, and I have suggested on her profile that her relationship to William and Lucy FitzPiers be marked as uncertain. Arguably, Anne should be detached unless stronger evidence emerges.