The illegitimate son of Robert I, duke of Normandy, and Arletta, daughter of a tanner, he is sometimes called William the Bastard. He succeeded to the dukedom on his father's death in 1035. William and his guardians were hard pressed to keep down recurrent rebellions during his minority, and at least once the young duke barely escaped death.
In 1047, with the aid of Henry I of France, he solidly established his power. William is said to have visited England in 1051 or 1052, when his cousin Edward the Confessor probably promised that William would succeed him as king of England. Despite a papal prohibition, William married Matilda, daughter of Baldwin, count of Flanders, in 1053. The union, which greatly increased the duke's prestige, did not receive papal dispensation until 1059.
William's growing power brought him into conflict with King Henry of France, whose invading armies he defeated in 1054 and 1058. The accession (1060) of the child Philip I of France, whose guardian was William's father-in-law, improved his position, and in 1063 William conquered the county of Maine. Soon afterward Harold, then earl of Wessex, was shipwrecked on the French coast and was turned over to William, who apparently extracted Harold's oath to support the duke's interests in England.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.