William I

William I may refer to:

Kings

 * William the Conqueror (c. 1028–1087), also known as William I, King of England
 * William I of Sicily (died 1166)
 * William I of Scotland (died 1214), known as William the Lion
 * William I of the Netherlands and Luxembourg (1772–1843)
 * William I of Bimbia (fl. 1850s)
 * William I of Württemberg (1781–1864)
 * William I, German Emperor (1797–1888)

Nobles

 * William I of Gascony (died 848)
 * William I of Aquitaine (died 918)
 * William I of Montferrat (fl. 924)
 * William I of Normandy (c. 900–942)
 * William I of Montpellier (fl. 980s)
 * William I of Provence (c. 950–993)
 * William I Talvas (c. 995–after 1030), seigneur of Alençon
 * William Iron Arm (before 1010–1046), Duke of Apulia
 * William I, Bishop of Utrecht (died 1076)
 * William I, Count of Nevers (c. 1030–after 1083)
 * William I, Count of Burgundy (1020–1087)
 * William de Warenne, 1st Earl of Surrey (died 1088)
 * William I of Cerdanya (1068–1095)
 * William I of Bures (died 1142), French crusader
 * William I of Béarn (died 1173)
 * William le Gros, 1st Earl of Albemarle (died 1179)
 * William I of Geneva (fl. 1190s)
 * William of Champlitte (died 1209), Prince of Achaea
 * William I of Cagliari (c. 1160–1214)
 * William I, Lord of Douglas (died c. 1214)
 * William I, Count of Holland (c. 1167–1222)
 * Uilleam I, Earl of Ross (died 1274)
 * William I de la Roche (died 1287), Duke of Athens
 * William I, Count of Hainaut (1286–1337)
 * William I, Duke of Bavaria (1330–1389)
 * William I of Guelders and Jülich (1364–1402)
 * William I, Margrave of Meissen (1343–1407), known as William I, the one-eyed
 * William I, Landgrave of Hesse (1466–1515)
 * William I, Count of Nassau-Siegen (1487–1559)
 * William the Silent (1533–1584), Prince of Orange
 * Guglielmo I Gonzaga (1538–1587), Duke of Mantua
 * William I, Elector of Hesse (1743–1821)