William the Simple, Lord of Sully

William the Simple (c. 1085–c. 1150) was the eldest son of Count Stephen of Blois and Adela of Normandy, daughter of William the Conqueror. Designated Count of Blois and Chartres in 1102, he intervened in his mother's dispute with the cathedral chapter, bursting into the church to demand an oath against its canons. Around 1107 his mother set him aside in favour of his brother Theobald.

He married Agnes, heiress of Sully-sur-Loire, and retired to her Sully estates. Though the Conqueror's eldest legitimate grandson, he was never advanced for the English crown; King Stephen was his brother and Eudes Archambaud his son.