[1] His mother, Adela of Flanders, had previously been queen of Denmark, and he was a half-brother of Charles the Good.
He succeeded his father as duke in 1111,[1] though Adela served as regent until William was of age.
He died without legitimate posterity in July 1127, leaving the entire of the Norman Mezzogiorno to be seized by his first cousin once removed, Roger II of Sicily, his erstwhile ally.
[3] According to the Fragmentary Troia Chronicle, William journeyed to the capital of the Byzantine Empire in 1116, but this is implausible.
[4] Considered an insignificant ruler by dated historiography, William was respected by his contemporaries, popular with his barons and subjects, and praised for his martial prowess.