Pope Callixtus III, born Alfonso de Borgia, was head of the Catholic Church and ruler of the Papal States from 8 April 1455 to his death, in August 1458.

Alfonso the Magnanimous was King of Aragon and King of Sicily and the ruler of the Crown of Aragon from 1416 and King of Naples from 1442 until his death. He was involved with struggles to the throne of the Kingdom of Naples with Louis III of Anjou, Joanna II of Naples and their supporters, but ultimately failed and lost Naples in 1424. He recaptured it in 1442 and was crowned king of Naples. He had good relations with his vassal, Stjepan Kosača, and his ally, Skanderbeg, providing assistance in their struggles in the Balkans. He led diplomatic contacts with the Ethiopian Empire and was a prominent political figure of the early Renaissance, being a supporter of literature as well as commissioning several constructions for the Castel Nuovo.