Facts and Events
William Malet (died 1071) is one of the very few proven Companions of William the Conqueror known to have been present at the Battle of Hastings in 1066, as recorded by the contemporary chronicler William of Poitiers (c. 1020-1090). He held substantial property in Normandy, chiefly in the Pays de Caux, with a castle at Graville-Ste-Honorine, at the mouth of the River Seine near Harfleur (nowadays a suburb of Le Havre).
From Mallett Family History Site - 
William Malet, or Guillaume, as he may have been called, "Sire de Graville", came from Graville Sainte Honorine between Le Havre and Harfleur, in what is today the French province of Normandy. He is said to have had a Norman father and a Saxon (read English) mother, and had some sort of association with King Harold of England before the conquest. William, through his Saxon mother, may actually have been related to King Harold, and also to the well known Lady Godiva. It is also possible that William and Harold were both God fathers of Duke William of Normandy's daughter, Abela. The Malet Castle at Graville Sainte Honorine had an important strategic location, at the mouth of the Seine. It has now fallen into the sea, though some remnants of it may still be visible. A large section of wall with large iron rings attached was still there just over 100 years ago. The Abbey church, in which some of the Malets are buried, is now in the town of Le Havre. Though William Malet had connections to both sides in the conflict to come, his main allegiance was to Duke William of Normandy.
William fought with distinction at Hastings, as the following Excerpt from Wace's "Roman de Rou" attests:
When the battle was over, Duke William entrusted William Malet to attend to the burial of the dead English king. The body was buried under a heap of stones on top of a cliff at Hastings overlooking the shore that Harold had so bravely defended. William placed a stone on the grave with the epitaph:
William and his brother Durand held lands in Lincolnshire, England, during the reign of Edward the Confessor, and through the reign of Harold right up to the conquest, in addition to those in Normandy. These Lincolnshire holdings, all in the Danelaw, probably came from William and Durand's mother. After the conquest William's English holdings were greatly increased, again, principally in the Danelaw, as English lands were taken from their Saxon owners and handed over to Norman Barons. It is likely that Duke William conferred these estates on William, partly because of his loyalty and skill in battle, but also because of his prior connections with his Danish "cousins" there. Perhaps the Duke felt that William was the best man to bring these proud, warlike and independent settlers under the control of their new King.
William was dead at the time of the Domesday survey in 1086, but the holdings at that time of his son Robert, and of his wife, give a good indication of the extent of his estates. He held large parts of what are today Suffolk and Norfolk, with smaller amounts of land in Lincolnshire and Yorkshire. Eye, in Suffolk appears to have been William's stronghold. Here he built a Motte and Bailey castle, after the Norman fashion. Nothing remains of the Norman fortifications, but the outline of the baileys and "Castle Mound", are still evident. There is even a slight indication of where the Market, founded by William Malet under Royal License would have been held.
William married Hesilia Crispin, by whom he had two sons, Robert and Gilbert, and one daughter, Beatrice. Robert and possibly Gilbert, along with their uncle Durand, accompanied their father at the battle of Hastings. The arms shown at the top of the page, likely carried by the Malets at Hastings, were used by many generations of the Malet family, both in England and in France, and can be seen on the Bayeux tapestry.
William was made Sheriff of York and granted considerable lands in Yorkshire following the building of the first Norman castle there (the mound now supports 'Clifford's Tower') in 1068. He and his fellow captains, Robert Fitz-Richard and William of Ghent, with 500 picked knights had to fight off a local revolt, headed by Edgar the Atheling; this in or shortly after January 1069. Robert Fitz-Richard and many of his men were killed and it was only by the timely arrival of King William that the City was saved. The natives remained restless and had another, token go, as soon as King William left but were quickly put down. The troops were strengthened and another castle built on the other side of the river from the original but, notwithstanding, in September 1069, William, his wife and two of his children were captured by a combined force of Danes and English under Sweyn of Denmark supported by Earls Waltheof and Gospatric and the Northumbrians, when York fell to them after a terrible fight. This led to King William ordering the burning and killing of everything in the north and Domesday, even 16 years later, records most of northern England as still being waste and uninhabited.
William, his wife and two children must have been released some time later and William retained most of his lands apart from those in Yorkshire, which will have come with the office of Sheriff, which had been taken from him. At some point the King awarded William the appellation of "Princep", and in the Chart granted by the King to the church of St. Martin le Grand, his signature appears as "Wilielmus Malet Princep". In the context of the times, Princep would likely have been interpreted as "leader, or chief". William is believed to have died fighting "Hereward the Wake" in the Fens near Ely Cathedral, which lies between South Lincolnshire, Cambridgeshire and Norfolk (and in the middle of the Malet holdings), in 1071. The Domesday book records that "...He went into the marsh", and that "...he went on the King's service, where he died".
William is generally accepted to be the progenitor of many of the various branches of the Malet family (those that can trace their lines back that far), both in England and in France. The descendants of Durand continued to hold lands in Lincolnshire, and are recorded in Irby on Humber up to the 16th century.
From Vol II File 16: The Paternal Ancestry of Homer Beers James 
Lord Malet, a Norman baron, one of the generals and companions of William the Conqueror, said to have been the brother of King Harold's wife, and to have been entrusted with the guard of Harold's body after he had been slain on the battlefield. After the conquest he was made Governor of York Castle and was slain in its defense about 1071. He married Hesila (Esilia) Crispin, daughter of Gilbert Crispin I, baron of Tillieres. She probably married (2) Alured de Lincoln, a great Domesday baron who attended Duke William on his expedition to England in 1066 (See Crispin and Macary, "Falaise Roll", Appendix 20, pg. 156-160).
Crispin and Macary
According to Crispin and Macary, "William (Guillaume) Malet de Graville stands out as one of the most imposing figures at the Conquest. There can be no doubt about his presence there, which is subscribed to be William of Poitiers, Guy of Amiens, Orderic Vital, and all the historians of this epoch. So much has been placed on record concerning him that just a few facts of his life will be recited here. He was probably descended from Gerard, a Scandinavian prince and companion of Duke Rollo, which gave the name of the fief of Gerardville or Graville, near Havre. Robert, the eldest son, occurs in a document of about 990 in Normandy. On his mother's side William Malet was of Anglo-Saxon origin, for she was probably the daughter of Leofric, Earl of Mercia, and Godwa or Godgifu, the supposed sister of Thorold the Sheriff in the time of Edward the Confessor, and therefore the aunt of Edwin and Morcar, Earls of Northumberland. He was nearly killed in the battle of Hastings but was rescued by the sire de Montfort and William of Vieuxpont, and was appointed by William the Conqueror to take charge of the body of Harold, a statement that has been disputed. The consensus of opinion favors it, and it is most logical if William Malet's mother was as stated the sister of Algar II., 7th Earl of Mercia, who was the father of Alditha, wife of Harold. He accompanied King William at the reduction of Nottingham and York in 1068, for which he was rewarded with the shreivalty of land in that county. Gilbert de Gand and Robert Fitz Richard were also commanders in this expedition. The following year he was besieged in the castle of York by Edgar, the Saxon prince, and was only saved from surrender by the timely arrival of the Conqueror. In the same year he was attacked by the Danes, who captured the city of York with great slaughter and took William Malet, his wife and children, prisoners, but their lives were spared, as was that of Gilbert de Gand, for the sake of their ransoms. There is evidence that he was slain in this year, but it is uncertain and the date of his death is unknown. An entry in Domesday that "William Malet was seized of this place (Cidestan, Co. Suffolk), where he proceeded on the King's service where he died," would indicate that his death occurred during the compilation of that book. He was witness to a charter of King William to the church of St. Martin-le-Grand, in London, and is there styled "princeps," which title, however, was honorary and not hereditary, having ceased with his death."