William the Conqueror, sometimes called William the Bastard, was the first Norman king of England, reigning from 1066 until his death. A descendant of Rollo, he was Duke of Normandy from 1035 onward. By 1060, following a long struggle to establish his throne, his hold on Normandy was secure. In 1066, following the death of Edward the Confessor, William invaded England, leading an army of Normans to victory over the Anglo-Saxon forces of Harold Godwinson at the Battle of Hastings, and suppressed subsequent English revolts in what has become known as the Norman Conquest. The rest of his life was marked by struggles to consolidate his hold over England and his continental lands, and by difficulties with his eldest son, Robert Curthose.

Rollo was a Viking who, as Count of Rouen, became the first ruler of Normandy, a region in today's northern France. He emerged as a leading warrior figure among the Norsemen who had secured a permanent foothold on Frankish soil in the valley of the lower Seine after the Siege of Chartres in 911. Charles the Simple, king of West Francia, granted them lands between the mouth of the Seine and what is now Rouen in exchange for Rollo agreeing to end his brigandage, swearing allegiance to him, religious conversion and a pledge to defend the Seine's estuary from other Viking raiders.