William of Montferrat is the name of: William I of Montferrat (d. before 933) William II of Montferrat (died probably around 961) William III of Montferrat (991 – bef.1042), son of Otho I William IV of Montferrat (c.1084–c.1100) William V of Montferrat (c.1136–1191) William Longsword of Montferrat (c. 1140–1177) William VI of Montferrat, (1207–1225) William of Montferrat (monk), 13th century William VII of Montferrat (c.1255–1292), titular king of Thessalonica William VIII of Montferrat (1464–1483) William IX of Montferrat (1494–1518), see Casale Monferrato William X of Montferrat, 1st duke of Montferrat, Duke of Mantua