William I c. 1028 – 9 September 1087), usually known as William the Conqueror and sometimes William the Bastard, son of the unmarried Robert I, Duke of Normandy, by Robert's mistress Herleva.William was the first Norman King of England, reigning from 1066 until his death in 1087. A descendant of Rollo, he was Duke of Normandy from 1035 onward. After a long struggle to establish his power, by 1060 his hold on Normandy was secure, and he launched the Norman conquest of England six years later.