William was born as the illegitimate son of Robert I, Duke of Normandy, and Herleva, a tanner's daughter. His birth outside marriage would earn him the nickname 'William the Bastard.'

When his father died on pilgrimage to Jerusalem, the young William became Duke of Normandy at age seven. His minority was marked by violence and instability among Norman nobles.

Young William survived multiple assassination attempts by rival nobles. His guardian Osbern was murdered, and William had to be hidden by loyal supporters to preserve his life.

With help from King Henry I of France, William defeated rebel Norman barons at Val-ès-Dunes. This victory established his authority as Duke of Normandy and ended the threats to his rule.

William strengthened his position through strategic castle-building and marriage alliances. He developed the Norman military system that would later prove decisive in conquering England.

During a visit to his cousin Edward the Confessor, William allegedly received a promise of succession to the English throne. This claim would later justify his invasion of England.

William married Matilda of Flanders despite papal opposition due to their close kinship. The marriage strengthened ties with Flanders and produced at least nine children including two future kings.

William decisively defeated an invasion force led by King Henry I of France at Varaville. This victory ended French attempts to subdue Normandy and secured William's independence.

Harold Godwinson, later King of England, allegedly swore an oath over holy relics to support William's claim to the English throne. Breaking this oath would justify William's invasion.

William landed his invasion force of approximately 7,000 soldiers at Pevensey Bay on September 28. He quickly established a base camp and fortifications before marching inland.

On October 14, William defeated King Harold II at the Battle of Hastings. Harold was killed, reportedly by an arrow to the eye, ending Anglo-Saxon resistance to the Norman invasion.

On Christmas Day, William was crowned King of England at Westminster Abbey. His coronation established Norman rule over England and began a new era in English history.

William marched north to suppress rebellions in Exeter and York. He built castles throughout the realm to establish Norman control and suppress any remaining Anglo-Saxon resistance.

In response to continued rebellion, William devastated Northern England in a brutal campaign. Villages were destroyed and crops burned, causing widespread famine and death.

William began construction of the White Tower, the central keep of the Tower of London. This fortress symbolized Norman power and served as a royal residence and prison.

William arrested his half-brother Odo, Bishop of Bayeux, for raising an army without permission. This demonstrated William's commitment to maintaining royal authority even over family.

William commissioned the Domesday Book, a comprehensive survey of landholdings throughout England. This remarkable administrative achievement recorded the wealth and resources of his kingdom.

William died from injuries suffered when his horse stumbled during the sack of Mantes. He was buried at the Abbaye-aux-Hommes in Caen, which he had founded.