William IV, 1765–1837, king of Great Britain and Ireland (1830–37), third son of George III. He went to sea in 1779, served under Admiral George Rodney in action off Cape St. Vincent (1780), and by 1786 was a captain. William became duke of Clarence in 1789 and was advanced by 1799 to the rank of admiral, but he saw little active service after 1790. Meanwhile in the House of Lords he opposed the antislavery movement and supported the extravagances of his oldest brother (later George IV). About 1791 he formed a liaison with Mrs. Jordan, an actress, with whom he lived for over 20 years. He married (1818) Adelaide, daughter of the duke of Saxe-Meiningen, and on the death (1827) of the duke of York, second son of George III, he became heir presumptive to the throne. Made lord high admiral in 1827, he tried to run naval affairs without his council, contrary to law, and was forced to resign (1828). In 1830 he succeeded George IV as king. His most important public act was his promise, given most reluctantly, to the 2d Earl Grey that he would, if necessary, create enough Whig peers to pass the Reform Bill of 1832 (see under Reform Acts). This bill and such reforms as the education act, the new poor law, the municipal corporations act, and the abolition of slavery in the empire marked his reign, but he maintained the generally passive attitude toward politics formed during his many years as younger son and later younger brother of the king. Political leadership was left to the duke of Wellington, Earl Grey, Viscount Melbourne, and Sir Robert Peel. Good-natured but eccentric and given to ill-considered public utterances, William was only moderately popular. He was succeeded by his niece, Victoria.
See biographies by W. G. Allen (1960) and P. Ziegler (1971).