William FitzAlan, Lord of Oswestry

William FitzAlan (1105–1160) was a nobleman of Breton ancestry. He was a major landowner, a Marcher lord with large holdings in Shropshire, where he was the Lord of Oswestry, as well as in Norfolk and Sussex. He took the side of Empress Matilda during the Anarchy and underwent considerable hardship in the Angevin cause before regaining his lands and former status. William's younger brother, Walter fitz Alan (d. 1177), became ancestor of the royal House of Stuart.

William was born around 1105. He was the eldest son and heir of Alan fitz Flaad, a Breton noble whose family were closely associated with the sacred environs of Dol-de-Bretagne, close to the border with Normandy and a short distance south-west of the great abbey of Mont Saint-Michel. Alan was a close ally of Henry I of England (1100-1135), who was determined to insert reliable supporters into strategically key areas after the disloyalty of Robert of Bellême, 3rd Earl of Shrewsbury, who had a strong support network in the Marches. Alan received extensive fiefs in Shropshire and Norfolk from around the beginning of Henry's reign and more as he proved his worth. Much of the Shropshire land was taken from the holdings of Rainald de Bailleul, ancestor of the House of Balliol, as was land around Peppering, near Arundel in Sussex.

William's mother was Avelina de Hesdin. Her father was Ernulf de Hesdin (also transcribed as Arnulf), a crusader baron from Hesdin in Artois, which was a fief of the County of Flanders and only loosely attached to France. Ernulf built up large holdings in Staffordshire and Gloucestershire. After his death in the First Crusade, Aveline's brother, also called Ernulf, inherited his lands and titles.