Mortain, Robert, Count of - Half-brother of William I, younger brother of Odo of Bayeux. Married Earl Hugh of Chester's daughter. Lord of the Sussex rape of Pevensey, with castle there. Virtual Earl of Cornwall; fief included Honour of Berkhamsted with castle there. Rebelled 1088; pardoned; died 1091. Largest landholder in the country after the King. Holdings in 19 counties.