William FitzOsbern , 1st Earl of Hereford William FitzOsbern ( circa 1020 – 22 February 1071 ) , Lord of Breteuil , in Normandy , was a relative and close counsellor of William the Conqueror and one of the great magnates of early Norman England . He was created Earl of Hereford before 22 February 1067 , one of the first peerage titles in the English peerage . Background . He was the son of Osbern the Steward , a nephew of Duchess Gunnor , the wife of Duke Richard I of Normandy . Osbern had been the steward of his cousin Duke Robert I of Normandy , and when Robert left the Duchy to his young son William , Osbern had been one of Duke William ' s guardians , but was killed defending the person of Duke William against an assassination attempt sometime around 1040 . Osbern had married Emma , a daughter of Count Rodolf of Ivry , who was a half - brother of Duke Richard I of Normandy . Through her he inherited a large property in central Normandy , including the honours of Pacy and Breteuil . Early life . William FitzOsbern was probably raised at the court of his cousin and namesake Duke William , and like his father , became one of the ducal stewards . As a Norman nobleman , he founded or helped to found the monasteries of Cormeilles and Lyre on his lands , and gave the abbey in the land of Ouche the church and land of Saint - Evroul - Notre - Dame - du - Bois . He was one of the earliest and most vigorous advocates of the invasion of England , and tradition holds that he convinced the doubters amongst the Norman barons of the feasibility of the invasion . He is one of the very few proven Companions of William the Conqueror known to have fought at the Battle of Hastings in 1066 . FitzOsbern ' s younger brother Osbern was one of Edward the Confessor ' s chaplains , and possessed the rich church of Bosham in Sussex , and was well - placed to pass along intelligence on the situation in England . He later became Bishop of Exeter . In England after 1066 . As Duke William took control of England ( becoming William I of England ) , FitzOsbern was given charge of the Isle of Wight , and then before 22 February 1067 he was made Earl of Hereford as well as Gloucester , Worcester and Oxfordshire . That part of England was not yet fully under Norman control ; the understanding must have been that FitzOsbern was to take charge of their conquest when he was able . In the summer of 1067 the King returned to Normandy , leaving FitzOsbern and Bishop Odo of Bayeux in charge of England in his absence . The King was back in England in 1068 , and fitzOsbern accompanied him in the subjugation of southwest England . He attended the King ' s Whitsun court in May , and then himself paid a visit to Normandy , where he fell ill for some months . In February or March 1069 FitzOsbern was given charge of the new castle at York , but he returned south in time to attend the King ' s Easter court in April . Anglo - Saxon resistance in the West Midlands was subdued later in 1069 , and it is likely FitzOsbern played a major part in this , though the details are not certain . During this time FitzOsbern and his followers pushed on into Wales , beginning the conquest of the Welsh Kingdom of Gwent . Castle builder . As part of the assertion of Norman control over England ( and Wales ) , FitzOsbern was one of the major Norman castle builders . Early castles attributed to him include Carisbrooke on the Isle of Wight and then in South Wales Chepstow ( Striguil ) , Wigmore , Clifford Castle , Berkeley Castle and Monmouth Castle , as well as creating or improving the fortification s of the towns of Hereford and Shrewsbury . Distraction and death in Flanders . In 1070 trouble arose in Flanders , where King William ' s brother - in - law Baldwin VI of Flanders had died , leaving his county and his young sons in the hands of his widow Richilde , Countess of Mons and Hainaut . Her control of Flanders was challenged by the brother of her late husband , Robert the Frisian . Looking for help , she offered herself in marriage to fitzOsbern . He could not resist the chance to become also Count of the rich Principality in the German Empire , close to Normandy . He hurried there with his army , but nevertheless was defeated by the Count of Flanders , losing his life in the Battle of Cassel on 22 February 1071 . Personal life . FitzOsbern married first Adeliza de Tosny , daughter of Roger I of Tosny . One assumes that he also married Richilde shortly before the Battle of Cassel . He was succeeded in Normandy by his eldest son , William of Breteuil and in England and Wales by his younger son , Roger de Breteuil . His daughter Emma married Ralph de Gael , 1st Earl of Norfolk . His son William of Breteuil ( d . 1103 ) was held captive and tortured by Ascelin Gouel de Perceval ' Lupus ' , Sire d ' Yvry , until he finally granted his daughter Isabella de Breteuil ' s hand in marriage to him . William FitzOsbern lived in Carisbrooke Castle .