Duke of Normandy (1035-1087), King of England (1066-1087).
William was the last ruler of England to face a major Scandinavian invasion. The illegitimate son of Robert the Magnificent, William succeeded his father as Duke of Normandy while still a child. On attaining his majority (c1042) he successfully established his authority in the face of baronial opposition. It is likely that the pro-Norman king Edward the Confessor had promised William the English throne, but on his death in 1066 the English chose Harold Godwinson as their king instead. Invading England, William defeated and killed Harold at Hastings (14 November 1066). William was fortunate that Harold's army had not had time to recover from its victory over a third claimant to the English throne, Harald Hadrada of Norway at Stamford Bridge less than three weeks before. He was crowned king of England on Christmas day 1066. William faced many uncoordinated rebellions during the early years of his reign, prompting interventions by the Danish king Svein Estrithson, who had inherited Harald Hardrda's claim to the English throne. In October 1069, a fleet of 240 Danish ships under Svein's son Cnut (Cnut II) allied with English rebels and took York. William recaptured York in December and spent the winter engaged in the infamous 'Harrying of the North'. As well as punishing the locals for supporting the rebels, this scorched-earth campaign was intended to make the area unattractive to further Danish intervention. Svein met his son on the Humber in spring 1070 and in June they joined Hereward the Wake in sacking Petersborough. But English resistance was collapsing and William was able to negotiate Sven's withdrawal. A second Danish intervention came in 1075 when Cnut was invited to take the English throne by rebel Norman barons. William had crushed the rebellion by the time Cnut arrived. William faced the threat of a third Danish Intervention in 1085 when Cnut, now king of Denmark, began to prepare an expedition to conquer England. The attack never materialised because Cnut was assassinated the following year. It was partly in response to this threat that William ordered the famous Doomsday survey in 1086. He was killed the following year when fighting in France.
Although William was of Scandinavian descent, the Norman conquest of England can in no way be considered as an extension of Viking activity: William and his followers were culturally and linguistically completely French. The conquest led to a decline of cultural and political links between England and Scandinavia as English institutions were Normanized and English culture was exposed to powerful French influences.
Notes from Encyclopaedia of the Viking Age by John Haywood. Thames
& Hudson 2000. pp 209-210.