William the Conqueror began life as William the Bastard, the illegitimate son of Robert I, Duke of Normandy. Robert died during his return from a pilgrimage to Jerusalem, leaving the 8-year-old William as his heir. William successfully gained the support of the French king, Henry I, and ascended to his father's office.
In 1066, at the age of 38, William led an army across the English Channel to conquer England. He succeeded in this endeavor, defeating an Anglo-Saxon force at the Battle of Hastings, and was crowned King of England in 1087. The dynasty he founded first ruled as an occupation force but eventually intermarried with the native gentry and became Anglicized. William's government introduced feudalism to England along with a civil code of laws that largely supplanted the earlier Anglo-Saxon system. It also established French as the language of the English court. The Norman influence would eventually craft a fusion between English and Norman French that became the English language.
William became the first monarch to organize a full census of England, which became known as the Domesday Book. He also reorganized land ownership, tax law and property rights. William, who never learned English, eventually returned to France and died of wounds suffered at Mantes in 1087.