Gregory X

Pope Gregory X (Latin: Gregorius X; born Teobaldo Visconti; c. 1210 – 10 January 1276) was head of the Catholic Church and ruler of the Papal States from 1 September 1271 to his death and was a member of the Third Order of St. Francis. He was elected at the conclusion of a papal election that ran from 1268 to 1271, the longest papal election in the history of the Catholic Church.

He convened the Second Council of Lyon and also made new regulations in regards to the papal conclave. Gregory was beatified by Pope Clement XI in 1713 after the confirmation of his cultus.

Gregory's regulations on the conduct of the conclave, though briefly annulled by Adrian V and John XXI, remained standard practice until the 20th century. Gregory's rules were dispensed in certain extraordinary circumstances, offering greater latitude in regulating an upcoming conclave, such as by Pope Pius VI in 1798, in consideration of the occupation of Rome by the French, and by Pope Pius IX in 1878, fearing a potential Vatican invasion could prevent or dominate a papal election.