Ferdinand II (10 March 1452 – 23 January 1516), called the Catholic, was in his own right the King of Sicily from 1468 and King of Aragon (the Aragonese crown included the kingdoms of Majorca, Sardinia and Valencia), as well as the Principality of Catalonia. from 1479. As Ferdinand V he was the King of Castile in his right of his wife, Isabella I, from 1475 until her death in 1504. He was recognised as regent of Castile for his daughter and heir, Joanna of Castile (Wikipedia page https://en.wikipedia.org/wiki/Joanna_of_Castile), from 1508 until his own death. In 1504, after a war with France, he became King of Naples as Ferdinand III, reuniting Naples with Sicily for the first time since 1458. In 1512, he became King of Navarre by conquest after asserting a hereditary claim.
Ferdinand is today best known for his role in inaugurating the discovery of the New World (Wikipedia page [1]), since he and Isabella sponsored the first voyage of Christopher Columbus in 1492. That year he also fought the final war with Granada which expunged the last Islamic state on Spanish soil, thus bringing to a close the centuries-long Reconquista. At his death he was succeeded by Joanna, who co-ruled with her son, Charles V (Wikipedia page [2]), over all the Iberian kingdoms (save Portugal).
More information on the Wikipedia page [3].