Frederick II (or III) (13 December 1272 – 25 June 1337) was the regent (from 1291) and subsequently King of Sicily from 1295 until his death. He was the third son of Peter III of Aragon and served in the War of the Sicilian Vespers on behalf of his father and brothers, Alfonso and James. He was confirmed as King of Trinacria (another name for the island of Sicily) by the Peace of Caltabellotta in 1302. His reign saw important constitutional reforms: the Constitutiones regales, Capitula alia, and Ordinationes generales.

Frederick III (or IV) (1 September 1341 – 27 January 1377), called the Simple, was King of Sicily  from 1355 to 1377. He was the second son of Peter II of Sicily and Elisabeth of Carinthia. He succeeded his brother Louis. The documents of his era call him the "infante Frederick, ruler of the kingdom of Sicily", without any regnal number.