William I, also known as William the Conqueror, was the first Norman King of England. After the death of Edward the Confessor, William claimed the English throne and invaded from Normandy. He defeated the Anglo-Saxon King Harold II at the Battle of Hastings, forever changing the course of English history. William's conquest brought French language, culture, and feudalism to England, leading to the development of the modern English language. He also commissioned the 'Domesday Book,' a comprehensive survey of all land and property in England for taxation purposes. His reign saw the construction of numerous stone castles, including the Tower of London. The Norman Conquest remains the most significant event in the shaping of English national identity and its medieval political structure.