William I, called the Bad or the Wicked, was the second king of Sicily, ruling from his father's death in 1154 to his own in 1166. He was the fourth son of Roger II and Elvira of Castile.

Roger II or Roger the Great was King of Sicily and Africa, son of Roger I of Sicily and successor to his brother Simon. He began his rule as Count of Sicily in 1105, became Duke of Apulia and Calabria in 1127, then King of Sicily in 1130 and King of Africa in 1148.