William was the eldest son of
Stephen, Count of Blois and
Adela of Normandy, daughter of
William the Conqueror. William was the older brother of
Theobald II, Count of Champagne;
Stephen, King of England; and
Henry, Bishop of Winchester. In the absence of male issue to
Henry I of England, William was the eldest legitimate grandson of William the Conqueror. He would thus have been the principal rival to Henry's daughter
Matilda to inherit the throne after Henry's death. However, William was not considered as a candidate for the
English crown. Several historians have taken the view that he was passed over because of mental deficiency; hence his soubriquet "William the Simple". Though widely argued, this has never been clearly substantiated. William was at first groomed to inherit the comital thrones of Blois and Chartres, and was designated count shortly before his father's departure on his second crusade in 1102. During his mother's dispute with the Chartres cathedral chapter (1102–1104), William burst in the cathedral demanding the burghers of Chartres take an oath to kill the canons, harass
Ivo of Chartres, and secure episcopal lands. William was soon removed from wide-ranging comital duties by his mother, and when her second son Theobald came of age, around 1107, Adela elevated him to the position of Count of Blois-Chartres. William retired to his wife's lands in
Sully. Despite his removal from comital duties, he supported his brother Theobald's familial ambitions. ==Marriage==