William de Mohun of Dunster, Earl of Somerset (c. 1090 – c. 1155), 2nd feudal baron of Dunster, was a favourite of Empress Matilda and a loyal supporter of her in the war against King Stephen, during which he earned the epithet of the "Scourge of the West".
[1] 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.
[1][2] Empress Matilda conferred upon him the title Earl of Somerset, in 1141.
In the foundation charter of the priory at Bruton[3] , he describes himself as "Willielmus de Moyne, comes Somersetensis".
[1] 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.