The office of the pope is the papacy. His ecclesiastical jurisdiction, the Diocese of Rome, is often called the "Holy See" or the "Apostolic See", the latter name being based on the belief that the Bishop of Rome is the apostolic successor to Saint Peter. The pope is considered one of the world's most powerful people because of his extensive diplomatic and cultural influence.
The papacy is one of the most enduring institutions in the world and has had a prominent part in world history. In ancient times the popes helped spread Christianity, and intervened to find resolutions in various doctrinal disputes. In the Middle Ages, they played a role of secular importance in Western Europe, often acting as arbitrators between Christian monarchs. Currently, in addition to the expansion of the Christian faith and doctrine, the popes are involved in ecumenism and interfaith dialogue, charitable work, and the defense of human rights.
In some periods of history, popes, who originally had no temporal powers, accrued wide secular powers rivalling those of temporal rulers. However, in recent centuries the temporal authority of the papacy has declined and the office is now almost exclusively focused on religious matters. By contrast, papal claims of spiritual authority have been increasingly firmly expressed over time, culminating in 1870 with the proclamation of the dogma of papal infallibility for rare occasions when the pope speaks ex cathedra—literally "from the chair (of Saint Peter)"—to issue a formal definition of faith or morals.
The word pope derives from Greek πάππας meaning "father". In the early centuries of Christianity, this title was applied, especially in the east, to all bishops and other senior clergy, and later became reserved in the west to the Bishop of Rome, a reservation made official only in the 11th century. The earliest record of the use of this title was in regard to the by then deceased Patriarch of Alexandria, Pope Heraclas of Alexandria (232–248). The earliest recorded use of the title "pope" in English dates to the mid-10th century, when it was used in reference to Pope Vitalian in an Old English translation of Bede's Historia ecclesiastica gentis Anglorum.
The Catholic Church teaches that the pastoral office, the office of shepherding the Church, that was held by the apostles, as a group or "college" with Saint Peter as their head, is now held by their successors, the bishops, with the bishop of Rome (the pope) as their head.