Pope Clement X (Italian: Papa Clemente X; 13 July 1590 – 22 July 1676), born Emilio Bonaventura Altieri, was Pope from 29 April 1670 to his death in 1676. Emilio Boneventura Altieri was born in Rome in 1590, the son of Lorenzo Altieri and Victoria Delfin, a noble Venetian lady, sister of Flaminio Delfin, commander general of the Papal Armies, and of Gentile Delfin, bishop of Camerino. His brother was Giambattista Altieri. The Altieri family belonged to the ancient Roman nobility and had enjoyed the highest consideration at Rome for several centuries; they had occasionally contracted alliances with the Colonnas and the Orsinis. During earlier pontificates, the Altieri held many important offices and had been entrusted with several delicate missions. Altieri received a doctorate in law from the Roman College in 1611. After finishing his studies, he was named auditor of Giovanni Battista Lancellotti in 1623, in the nunciature of Poland. He was ordained April 6, 1624. On his return to Rome, he was named Bishop of Camerino, then governor of Loreto and of all Umbria. Pope Urban VIII (1623–44) gave him charge of the works designed to protect the territory of Ravenna from the unruly Po River. Pope Innocent X (1644–55) sent him as nuncio to Naples, where he remained for eight years. He is credited with the re-establishment of peace after the stormy days of Masaniello. Pope Alexander VII (1655–67) confided to him a mission to Poland. Pope Clement IX (1667–69) named him Superintendent of the Papal Exchequer (in charge of the Church's finances), and in 1667 his maestro di camera, and he was made Secretary of the Congregation of Bishops and Regulars. Just before his death, Clement IX made him a cardinal. He was then about seventy-nine years of age; and Clement IX, when making him a member of the Sacred College, said to him: "You will be our successor." After the funeral of Pope Clement IX, sixty-two electors entered into conclave on 20 December 1669. Forty-two votes were necessary, and due to the rivalry between the French and Spanish factions, heated discussion prevailed for four months. Giovanni Cardinal Conti was supported by twenty-two votes; Cardinal Rospigliosi, nephew of the late pope, had thirty, or, as some say, thirty-three, with two at the accesso, so that he needed only seven more votes to gain the tiara. Cardinal Cerri obtained twenty-three votes. At length the cardinals agreed to resort to the old expedient of electing a cardinal of advanced years, and proposed Cardinal Altieri, almost an octogenarian, whose long life had been spent in the service of the Catholic Church, and whom Clement IX, on the eve of his death, had raised to the dignity of the purple. The reason a prelate of such transcendent merits received the cardinalate so late in life seems to have been that he had waived his claims to the elevation in favour of an older brother. On 29 April 1670, the papacy was offered to him by fifty-nine cardinals present at the election; only two being against him. He, however, objected because of his age, for he was almost eighty, and exclaimed, "I am too old to bear such a burden." Pointing to Cardinal Brancaccio, Altieri said he was the cardinal whom they ought to elect. He persisted in refusing, protesting that he no longer had strength or memory; eventually, with tears he accepted, and out of gratitude to his benefactor, by ten years his junior, he assumed the name of Clement X. He was crowned on 11 May.

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