William FitzOsbern, 1st Earl of Hereford, Lord of Breteuil (c. 1011 – 22 February 1071), was a relative and close counsellor of William the Conqueror and one of the great magnates of early Norman England. FitzOsbern was created Earl of Hereford in 1067,[a] one of the first peerage titles in the English peerage. He is one of the very few proven companions of William the Conqueror known to have fought at the Battle of Hastings in 1066. His chief residence was Carisbrooke Castle on the Isle of Wight, one of many castles he built in England.

After William became King of England, FitzOsbern was made an earl, with major land holdings in Gloucestershire, Herefordshire, Oxfordshire, and the Isle of Wight, and smaller areas under his authority in Berkshire, Dorset, Wiltshire, and Worcestershire.[1] In the summer of 1067 King William returned to Normandy and left his half-brother Bishop Odo of Bayeux and FitzOsbern in charge of England during his absence.[1] The king was back in England in 1068 and FitzOsbern accompanied him in the subjugation of south-west England. He attended the King's Whitsun court in May 1068, and then visited Normandy, where he fell ill for some months.

Norman Conquest to 18th century Carisbrooke Castle The Norman Conquest of 1066 created the position of Lord of the Isle of Wight; the island was given by William the Conqueror to his kinsman William FitzOsbern. Carisbrooke Priory and the fort of Carisbrooke Castle were then founded. Allegiance was sworn to FitzOsbern rather than the king; the Lordship was subsequently granted to the de Redvers family by Henry I after his succession in 1100. A silver penny of Edward I, minted 1300-05, found on the island in 2011[47] For nearly 200 years the island was a semi-independent feudal fiefdom, with the de Redvers family ruling from Carisbrooke. The final private owner was the Countess Isabella de Fortibus, who, on her deathbed in 1293, was persuaded to sell it to Edward I. Subsequently, the island was under the control of the English Crown[48] and its Lordship a royal appointment.