1The name of two kings of England and two of Great Britain and Ireland.

1. 1.1 William I (c.1027–87), reigned 1066–87, the first Norman king of England; known as William the Conqueror. He invaded England and defeated Harold II at the Battle of Hastings (1066). He introduced Norman institutions and customs (including feudalism) and instigated the Domesday Book.
2. 1.2 William II (c.1060–1100), son of William I, reigned 1087–1100; known as William Rufus. William crushed rebellions in 1088 and 1095 and also campaigned against his brother Robert, Duke of Normandy (1089–96), ultimately acquiring the duchy. He was killed by an arrow while out hunting.
3. 1.3 William III (1650–1702), grandson of Charles I, husband of Mary II, reigned 1689–1702; known as William of Orange. In 1688 he deposed James II at the invitation of disaffected politicians and, having accepted the Declaration of Rights, was crowned along with his wife Mary.
4. 1.4 William IV (1765–1837), son of George III, reigned 1830–7; known as the Sailor King. Having served in the Royal Navy, he came to the throne after the death of his brother George IV. In 1834 he intervened in political affairs by imposing the Conservative Robert Peel as prime minister, despite a Whig majority in Parliament.