William IV (1765–1837; ) was King of the United Kingdom of Great Britain and Ireland and concurrently King of Hanover.
William IV or 4 may also refer to: William IV of Aquitaine (937–994) William IV of Provence (died 1030) William IV of Weimar or William, Margrave of Meissen (died 1062) William IV of Montpellier () William IV of Toulouse (–1094) William IV of Montferrat (–1100) William IV of Nevers (–1168) William IV of Forcalquier (1130–1208) William IV of Saint Omer (–1191) William IV of Ponthieu (1179–1221) William IV, Count of Jülich (–1278) William IV, Lord of Douglas (died 1333) William IV of Holland or William II, Count of Hainaut (1307–1345) William IV of Hainault or William II, Duke of Bavaria (1365–1417) William IV, Lord of Egmont (1412–1483) William IV, Duke of Brunswick-Lüneburg (–1503) William IV, Duke of Jülich-Berg (1455–1511) William IV, Princely count of Henneberg-Schleusingen (1478–1559) William IV, Duke of Bavaria (1493–1550) William IV, Landgrave of Hesse-Kassel (1532–1592) William IV, Prince of Orange (1711–1751) William IV, Grand Duke of Luxembourg (1852–1912)
See also Guillaume IV (disambiguation), the French equivalent of William IV King William (disambiguation) Prince William (disambiguation) William the Fourth (disambiguation) List of people with given name William#Royalty and nobility