Pedro Julião (John XXI) elected Pope

Pope John XXI (1215 – May 20, 1277; Portuguese: Papa João XXI), born Pedro Julião (Latin, Petrus Iulianus), a Portuguese also called Pedro Hispano (Latin, Petrus Hispanus), was Pope from 1276 until his death about eight months later. He was the only Portuguese Pope, although Damasus I can also be considered Portuguese, as he was born in territory that is nowadays in Portugal, and Paul IV also had a Portuguese maternal grandmother.
He was also a physician, being the only pope ever to be so.
Note that the previous Pope named John was Pope John XIX (1024–32) as there was no Pope John XX.

Pedro Julião, born between 1210 and 1220, was probably born in Lisbon. He started his studies at the episcopal school of Lisbon Cathedral, and later joined the University of Paris, although some historians claim that he was educated at Montpellier. Wherever he studied, he concentrated on medicine, theology, and Aristotle's dialectic, logic, physics and metaphysics.
From 1245 to 1250 he became known as Pedro Hispano (because he came from Hispania, the Iberian Peninsula) and taught medicine at the university of Siena, where he wrote the Summulae Logicales, a reference manual on Aristotelian logic that remained in use in European universities for more than 300 years (see Peter of Spain for some controversies). He became famous as a university teacher, then returned to Lisbon. In the courts of Guimarães he was the councilor and spokesman of the king Afonso III of Portugal (1248–79) in church matters; later, becoming prior of Guimarães. He tried to become Bishop of Lisbon, but he was defeated. Instead, he became the master of the school of Lisbon. A notable philosopher, he was also the responsible for the creation of the Square of opposition.
Pedro became the physician of Pope Gregory X (1271–76). In March 1273 he was elected archbishop of Braga, but did not assume that post because on June 3, 1273 Gregory X created him Cardinal-Bishop of Frascati.

After the death of Pope Adria...

Born at Lisbon between 1210 and 1220; enthroned, 1276; died at Viterbo, 20 May, 1277. The son of one Julianus, he was baptized Peter, and was known as Petrus Juliani or Petrus Hispanus. After his earlier studies in the cathedral school at Lisbon, he entered the University of Paris and attended lectures on dialectics, logic, and, more particularly, those on Aristotelean physics and metaphysics then being given by Albertus Magnus. The natural philosophy of Aristotle had a special attraction for Peter. He zealously pursued the study of medicine, and also that of theology, attaching himself especially to the Minorite magister, John of Parma. On completing his studies, he was called in 1247 as professor of medicine to the University of Siena, which was at that time being greatly enlarged. Here he wrote his "Summulæ logicales", for almost three hundred years the favourite textbook on logic. Stapper's investigations (see below) have now established beyond question the authorship of this work. In the fifteenth century the "Summulæ" was translated into Greek by George Scholarius, and was also translated into other languages. In content and form the book is based on the method current at the University of Paris, and on the compendium of William Shyreswood, Peter's professor there. While teaching at Siena, he also made a collection of medical prescriptions.
About 1261 Peter appears in the retinue of Cardinal Ottoboni Fieschi; towards this time also he was made deacon of the Church of Lisbon, an office which he later exchanged for the archidiaconate of Vermuy in the Diocese of Braga. From this period probably dates his acquaintance with Teobaldo Visconti. When, in 1272, Teobaldo came to Viterbo after his election to the papacy as Gregory X, he appointed Petrus Hispanus his physician in ordinary. While occupying this position, the latter wrote his "Thesaurus pauperum", in which he gives a remedy for the diseases of every part of the body. This book was widely used, but was i...

Pedro Juliano, or Peter of Spain, was born in Lisbon c. 1210/20. The son of a physician, he studied at the University of Paris and taught medicine at the University of Siena. He became cardinal bishop of Tusculum in 1273 and attended the Second Council of Lyons the following year. He was elected pope in 1276. He hoped to re-establish unity with the Eastern church but was in his nine-month papacy more concerned with fighting the influence of Averroism at the University of Paris and with an attempt to launch a crusade. Peter is the author of Summulae logicales, a treatise on logic, and The Poor Man's Treasury, a book of cures. He wrote a medical treatise on the eye, a book on the soul, and a commentary on The Celestial Hierarchy of Dionysios.