From the beginning of his reign, King Henry I of France was occupied with putting down rebellions led by members of his own family and other French nobles. Between 1035 and 1047, he assisted his nephew, William, Duke of Normandy (who would later become known as William the Conquerer) in establishing William’s authority over rebellious Norman nobles. Henry later grew jealous of William’s power and waged an unsuccessful war against him in 1054 and again in 1058.