Feudal barony of Dunster of Dunster, was as follows: William de Moyon (died post 1090) ("alias" de Moion, later de Mohun), Domesday Book holder of Dunster Castle, 1st feudal baron of Dunster, was Seigneur of Moyon near Saint-Lô in Normandy and was Sheriff of Somerset in 1086. He was the founder of the English "de Mohun" family, prominent in the Westcountry, extinct in the male line seated at Dunster in 1375 and extinct in the junior male line seated at Mohuns Ottery in Devon at about the same time. He is recorded in the Domesday Book of 1086 as holding the manor of "Torre"
Dunster Castle during the early 12th century, probably forming a shell keep around the top of the motte. In the late 1130s England began to descend into a period of civil war known as the Anarchy, during which the supporters of King Stephen fought with those of the Empress Matilda for control of the kingdom. William de Mohun's eldest son, also called William, was a noted supporter of Matilda, and Dunster was considered one of her faction's strongest castles in the south-west. In 1138 forces loyal to Stephen besieged the castle; a siege castle was built nearby, but all trace of it