William I

William I may refer to:

• William I, German Emperor (1797–1888)
• William the Conqueror, King of England 1066–1087 and Duke of Normandy 1035–1087
• William I of Scotland (died 1214), known as William the Lion
• William I of Sicily (died 1166)
• William I of the Netherlands and Luxembourg (1772–1843)
• William I of Württemberg (1781–1864)
• William I, Duke of Bavaria (1330–1389)
• William I, Elector of Hesse (1743–1821)
• William I, Landgrave of Hesse (1466–1515)
• William I, Margrave of Meissen (1343–1407), known as William I., the One-eyed
• William I, Count of Nassau-Dillenburg (1487–1559)