William de Mohun of Dunster, 1st Earl of Somerset William de Mohun of Dunster, 1st Earl of Somerset 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". 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
Dunster Castle and Colonel Robert Blake led a Parliamentary force against Dunster in October. In November Blake began his siege of the castle, setting up his artillery in Dunster village and starting to dig tunnels to plant mines beneath the walls. The castle was briefly relieved by reinforcements in February 1646, but the siege was resumed and by April the Royalists situation was untenable – an honourable surrender was negotiated and a Parliamentary garrison installed. After the end of the Second English Civil War in 1649, however, Parliament decided to deliberately destroy, or slight, the defences of castles in key Royalist areas,