Ferdinand II of Aragon (Fernando de Aragón in Spanish and Ferran d'Aragó in Catalan), nicknamed the Catholic (March 10, 1452 – June 23, 1516) was king of Aragon, Castile, Sicily, Naples and Navarre and Count of Barcelona.

He became Ferdinand V of Castile when he married Isabella I of Castile. They united their two kingdoms, running them as one country though they remained officially separate. He was also the king of Sicily (as Ferdinand II) from 1468 to 1516 and Naples (as Ferdinand III) from 1504 to 1516.

Their children included Joanna of Castile and Catherine of Aragon. Because of the power of their joint kingdoms, their daughters married with several European dynasties, setting the bases for the huge heritage of her grandson Charles V.

In November 1511 Ferdinand and Henry VIII of England signed the Treaty of Westminster, pledging mutual aid between the two against France. Earlier that year, Ferdinand had conquered the southern half of the Kingdom of Navarre and annexed it to Spain. Since he was a widower by then, he married Germana of Foix.

After Isabella left her kingdom to her daughter Joanna, Ferdinand served as her regent during her insanity. Though rebuffed by the Castilian nobility and replaced with Joanna's husband Philip I of Castile, he resumed his regency after Philip's death. Joanna's son, the Holy Roman Emperor Charles V, succeeded her on the throne of Castile; and he also succeeded Ferdinand on the Aragonese throne when Ferdinand died in 1516. Thereafter the thrones were united; see List of Spanish monarchs.

Some authors think that he was the inspiration for Niccolo Machiavelli's The Prince, although others do not.

See also

• Spanish Inquisition
• Monarchs of Naples and Sicily
• Cardinal Cisneros