Robert, Count of Mortain, first Earl of Cornwall of 2nd creation was a Norman nobleman and the half-brother of King William the Conqueror. He was one of the very few proven companions of William the Conqueror at the Battle of Hastings and as recorded in the Domesday Book of 1086 was one of the greatest landholders in his half-brother's new Kingdom of England.

William the Conqueror, sometimes called William the Bastard, was the first Norman king of England, reigning from 1066 until his death. A descendant of Rollo, he was Duke of Normandy from 1035 onward. By 1060, following a long struggle to establish his throne, his hold on Normandy was secure. In 1066, following the death of Edward the Confessor, William invaded England, leading an army of Normans to victory over the Anglo-Saxon forces of Harold Godwinson at the Battle of Hastings, and suppressed subsequent English revolts in what has become known as the Norman Conquest. The rest of his life was marked by struggles to consolidate his hold over England and his continental lands, and by difficulties with his eldest son, Robert Curthose.