William I
William I may refer to:
Kings
- William the Conqueror, also known as William I, King of England
- William I of Sicily
- William I of Scotland, known as William the Lion
- William I of the Netherlands and Luxembourg
- William I of Bimbia
- William I of Württemberg
- Wilhelm I, King of Prussia and later German Emperor
Nobles
- William I of Gascony
- William I of Aquitaine
- William I of Montferrat
- William I of Normandy
- William I of Montpellier
- William I of Provence
- William I Talvas, seigneur of Alençon
- William Iron Arm, Duke of Apulia
- William I, Bishop of Utrecht
- William I, Count of Nevers
- William I, Count of Burgundy
- William de Warenne, 1st Earl of Surrey
- William I of Cerdanya
- William I of Bures, French crusader
- William I of Béarn
- William le Gros, 1st Earl of Albemarle
- William I of Geneva
- William of Champlitte, Prince of Achaea
- William I of Cagliari
- William I, Lord of Douglas
- William I, Count of Holland
- Uilleam I, Earl of Ross
- William I de la Roche, Duke of Athens
- William I, Count of Hainaut
- William I, Duke of Bavaria
- William I of Guelders and Jülich
- William I, Margrave of Meissen, known as William I, the one-eyed
- William I, Landgrave of Hesse
- William I, Count of Nassau-Siegen
- William the Silent, Prince of Orange
- Guglielmo I Gonzaga, Duke of Mantua
- William I, Elector of Hesse