- Peter of Spain
- Petrus Hispanus
- Pedro Giuliano
Son of Julianus. Studied at the cathedral school at Lisbon, Portugal, and the University of Paris, France. Professor of medicine at the University of Siena in 1247. Scholastic philosopher. Author of , a text book used extensively for over three centuries. Attended the Council of Lyons with Pope Gregory X, where he was consecrated bishop. Archbishop of Braga, Portugal. Cardinal–bishop of Tusculum on 5 June 1273.
Elected the 187th pope, the only Portuguese yet chosen. Reigned only nine months. Worked to improve the wretched conditions of clerics in Portugal. Demanded that English King Edward I pay the papal tribute due since 1215. Worked for a Crusade with the aid of the Tatars. Temporarily reconciled the Eastern and Western Churches in a synod at Constantinople, 1277. Because he worked so hard to insure the rights of the Church and the clergy, many of the secular leaders who had opposed him used the pope‘s great learning, his knowledge of medicine and of healing to spread rumors that he was involved in black magic.
Due to confusion in the medieval listing of popes named John, he called himself John XXI instead of John XX, and this numbering is normally used.