Callixtus III, pope (April 8, 1455 - August 6, 1458), born Alphonso de Borgia, Jativa, Valencia, Spain (1378). His early career was spent as a professor of law at Lerida and then as a diplomat in the service of the kings of Aragon, especially during the Council of Basel. He became a cardinal after reconciling Pope Eugene IV with King Alfonso V of Aragon.
He was raised to the papal chair in 1455 at a very advanced age as a compromise candidate. He was feeble and incompetent. The great object of his policy was the urging of a crusade against the Turks, who had captured Constantinople in 1453, but he did not find the Christian princes responsive to his call despite his every effort. He made 2 of his nephews cardinals; one of the two, Rodrigo Borgia, later became Pope Alexander VI.
He died in 1458.