Alfonso the Magnanimous KG (also Alphonso; Catalan: Alfons) was the King of Aragon (as Alfonso V), Valencia (as Alfonso III), Majorca, Sardinia and Corsica (as Alfonso II), Sicily (as Alfonso I) and Count of Barcelona (as Alfonso IV) from 1416, and King of Naples (as Alfonso I) from 1442 until his death. He was one of the most prominent figures of the early Renaissance and a knight of the Order of the Dragon.
Born at Medina del Campo, he was the son of Ferdinand I of Aragon and Eleanor of Alburquerque. He represented the old line of the counts of Barcelona through the female line, and was on his father's side descended from the House of Trastamara, the reigning House of Castile. By hereditary right he was king of Sicily and claimed the island of Sardinia for himself, though it was then in the possession of Genoa. Alfonso was also in possession of much of Corsica by the 1420s.
There are no Sardinian kings named Alfonso with numbers 1 to 3. The Sardinian royal title did not have a specific line of succession and all Aragonese kings used their own primary titles.