William IX may refer to:
- William IX of Aquitaine (1071–1126)
- William IX, Count of Poitiers (1153–1156)
- William IX of Montferrat (1494–1518)
- Wilhelm, Duke of Jülich-Cleves-Berg (1516–1592)
- William I, Elector of Hesse (or Hesse-Cassel), also known as William IX, Landgrave of Hesse-Kassel, (1743–1821)
Famous quotes containing the word william:
“An illiterate king is a crowned ass.”
—Medieval English proverb.
Said by the chronicler William of Malmesbury to have been much used by King Henry I of England (1068-1135)