King of Castile and León (1474–1516), King of Aragon as Ferdinand II (1479–1516), King of Sicily (1468–1516), and King of Naples (1502–16). He was the son of John II of Aragon. In 1469 he married the future Isabella Iof Castile, a significant step towards Spanish unification. He succeeded to the throne of Aragon in 1479, and in the same year helped Isabella to win the war of succession in Castile (1474–79). They began to rule jointly in both kingdoms in 1481, and in 1492 annexed the conquered territory of Granada to Castile. On Isabella’s death in 1504, he was recognized as Regent of Castile for his daughter Joanna the Mad. He subsequently married Germaine de Foix (1506), and incorporated Navarre into Castile (1515), thus becoming personal monarch of all Spain from the Pyrenees to Gibraltar.

A ruthlessly realistic politician, he was especially successful in the conduct of foreign policy. He surrounded France with a network of allies and acquired Naples. At home he modernized Spain’s governmental institutions, vested in himself the grand masterships of the wealthy military orders, and won important ecclesiastical concessions from the papacy, including the Bull of 1478 authorizing the Spanish Inquisition, a powerful council to combat heresy, to be controlled by the crown.