William IV of the United Kingdom (1765–1837).

A possible regnal name for Willem-Alexander, Prince of Orange (born 1967), if and when he succeeds to the throne of the Netherlands.

William IV, Prince of Orange (1711–1751).

William IV, Landgrave of Hesse-Kassel (1532–1592).

William IV of Ponthieu (1179–1221).

William IV, Grand Duke of Luxembourg (1852–1912).

Wilhelm, Duke of Jülich-Cleves-Berg (1516–1592).

William IV, Duke of Bavaria (1493–1550).

William IV of Toulouse (c. 1040–1094).

William IV of Aquitaine (937–994).

William II, Duke of Bavaria-Straubing (ruled 1404–1417), also William IV of Hainault.

William IV, Lord of Douglas (died 1333).

William IV of Montferrat (1030–1100).

William, Margrave of Meissen (died 1062), also William IV of Weimar.

William II, Count of Hainaut (1307–1345), also William IV of Holland.

William IV, Duke of Brunswick-Lüneburg (died 1495 or 1503).

William IV of Provence (died 1030).