Francesco I Sforza
He was the second son of Marquis 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.