William FitzOsbern (c. 1020 – 22 February 1071), Lord of Breteuil, in Normandy, was a relative and close counsellor of William the Conqueror and one of the great magnates of early Norman England. FitzOsbern was created Earl of Wessex, a title which his son did not inherit. He was created Earl of Hereford in 1067, one of the first peerage titles in the English peerage. He is one of the very few proven companions of William the Conqueror known to have fought at the Battle of Hastings in 1066. His chief residence was Carisbrooke Castle on the Isle of Wight, one of many castles he built in England.