Born around 1028, William was the illegitimate son of Duke Robert I of Normandy, and Herleve (also known as Arlette), daughter of a tanner in Falaise. Known as 'William the Bastard' to his contemporaries, his illegitimacy shaped his career when he was young.
On his father's death in 1035, William was recognised by his family as the heir - an exception to the general rule that illegitimacy barred succession. His great uncle looked after the Duchy until 1037, and his overlord, King Henry I of France, knighted him at the age of 15.
From 1047 onwards, William successfully dealt with rebellion inside Normandy involving his kinsmen and threats from neighbouring nobles, including attempted invasions by his former ally King Henry I of France in 1054 (the French forces were defeated at the Battle of Mortemer) and 1057.
