William VIII Palaiologos (Italian: Guglielmo VIII Paleologo; 19 July 1420 – 27 February 1483) was the Marquess of Montferrat from 1464 until his death.
He was the second son of Marquess John Jacob, and inherited the Marquisate after the death of his elder brother John IV.
He obtained by Emperor Frederick III the territories lost to Savoy from 1435.
William served as condottiero for Francesco I Sforza of Milan and was later the tutor of the latter's son Galeazzo Maria.
When the latter was assassinated, William acted as moderator in the Duchy of Milan.
William married firstly, on 19 January 1465, Marie de Foix (d.1467), daughter of Gaston IV, Count of Foix; and secondly on 18 July 1469 Elizabetta Sforza (1456–1473), daughter of Francesco I Duke of Milan; and finally, on 6 January 1474, Bernarde de Brosse (d.17 February 1485).
He had no legitimate son.
By his second marriage, he had daughters:
Giovanna, married to Ludovico II del Vasto, Marquess of Saluzzo
Blanche of Montferrat, married to Charles I, Duke of Savoy.When he died in Casale Monferrato, he was succeeded by his brother Boniface III.