william, count of mortain
Tenant-in-Chief of Kingston Manor
William, born before 1084, was the son of Robert, Count of Mortain (the half-brother of William the Conqueror) and Maud de Montgomery, daughter of Roger de Montgomerie, 1st Earl of Shrewsbury. William succeeded his father as tenant-in-chief of his Yeovil lands on the latter's death in 1090.
From childhood, he harbored a bitter dislike for his cousin King Henry I and demanded from him his father's earldoms of Mortain and Cornwall as well as the Earldom of Kent that had been held by his uncle, Odo. Henry kept putting off William's demands for the earldom of Kent and instead offered him the hand of Queen Matilda's sister, Mary of Scotland. William rejected the offer and Henry continued to prevaricate over Kent.
Eventually Henry removed lands in Cornwall from William alleging that they had originally been misappropriated. In response William left for Normandy feeling indignant and resentful. He joined forces with Robert Curthose and attacked several of Henry's holdings, which gave the king abundant reasons to strip William of all his English honours and lands, including those at Yeovil, in 1104.
William was captured, along with Duke Robert, at the Battle of Tinchebrai in 1106 where, led by the king himself, Henry's knights won a decisive victory. Robert was imprisoned in England and then Wales until his death at Cardiff Castle in 1134. William was stripped of Mortain and was imprisoned for many years. In 1140 he became a Cluniac monk at Bermondsey Abbey.