William was the son of
William de Moion, who was seigneur of
Moyon which is close to
Saint-Lô. The elder William was
High Sheriff of Somerset in 1084. During the war between Matilda and Stephen, Stephen marched against Mohun's castle at Dunster, but finding it too hard to take, he left Henry de Tracy to keep Mohun under siege. Empress Matilda conferred upon him the title
Earl of Somerset, in 1141. In the foundation charter of the priory at Bruton , he describes himself as "Willielmus de Moyne, comes Somersetensis". Unlike
Baldwin de Redvers who was created
Earl of Devon by Matilda at around the same time, William's title was not recognised by Stephen or
Henry II, Matilda's son, and his descendants did not use the title. ==Family==