William was born in either 1027 or 1028 at Falaise, Duchy of Normandy, most likely towards the end of 1028. He was the only son of Robert I, son of Richard II. His mother Herleva was a daughter of Fulbert of Falaise, a tanner. Herleva was possibly a member of the ducal household, but did not marry Robert. She later married Herluin de Conteville, with whom she had two sons – Odo of Bayeux and Count Robert of Mortain – and a daughter whose name is unknown. One of Herleva's brothers, Walter, became a supporter and protector of William during his minority. Robert I also had a daughter, Adelaide, by another mistress.
In 1066, William invaded England with an army of Norman knights and infantry, landing in the south of England near Hastings. The English army, led by King Harold Godwinson, met William's forces in a fierce battle at Hastings on October 14, 1066. Despite being outnumbered, William emerged victorious and was crowned King of England on Christmas Day of the same year.