Ferdinand of Aragón was born on March 10, 1452 the son of Juana Enríquez. Ferdinand had an older half-brother, Carlos of Viana, who was the heir to the throne of Aragón. Carlos of Viana died making Fernando the rightful heir to the throne. Unlike Isabella, Ferdinand came to the throne completely undisputed. The kingdom of Aragón extended from the northern Pyrenees to eastern Granada in the south. The connection of Castile and Aragón created a united Spain. When Ferdinand married Isabella in 1469, he signed the Capitulations of Cervera. These agreements included never leaving Castile (or brining his children or Isabella out of Castile) without the permission of Isabella. Any decisions regarding political actions such as alliances and wars could not be made without consulting Isabella. These among other rules ensured that Isabella would remain in power of Castile and that Ferdinand could not take advantage of the country. The Kingdom of Aragón did not allow female succession and Isabella wanted to do everything it ensure that she remained in power and Ferdinand could not strip her of power.
Isabella and Ferdinand made an interesting match because of their differing personalities. In contrast to Isabella Fernando was known to be insensitive, deceitful, sly, and self-centered. While she was pious, faithful, and respected, he was not trusted and unreliable. At the same time, Fernando did have useful qualities. He was powerful and persuasive and he, like Isabella, was dedicated to bringing Spain to Glory. Ferdinand and Isabella became a unit in fighting for Spain’s Glory. This common goal made them a strong team even though their personal relationship was not perfect. Fernando had at least five illegitimate children; Isabella was able to look past his unfaithfulness and keep the marriage strong. Fernando went on to establish Spain with Isabella. He was involved in the execution of the Spanish Inquisition, the funding of Christopher Columbus’s voyage to America, the establishment of a new Justice System, the affirmation of the Church, and the glorification of Spain (Miller 56-74)

Miller, Townsend. The Castles and the Crown. New York: Capricorn Books, 1964.