List of Famous people named William

William of Ypres was a Flemish nobleman and one of the first mercenary captains of the Middle Ages. Following two unsuccessful bids for the County of Flanders, William became King Stephen of England's chief lieutenant during the civil war of 1139–54 known as the Anarchy. He held Kent, though not the title of earl, until the early years of King Henry II's reign, when he returned to Flanders.

William Isarn was the Count of Ribagorza from 1010 until his death in 1017 or 1018. He was a young man when he became party to a power-sharing agreement between his cousin and her husband, sponsored by the Count of Castile. He used a Castilian army to remove the Muslim garrisons from the valley of the Isábena, but before his work of Reconquista could be completed, he was assassinated while trying to reestablish his family's rights in the Val d'Aran. His death provoked a succession crisis that ended in the absorption of Ribagorza into the domains of the King of Navarre.