Ecclesiastical title of the bishop of Rome, head of the Roman Catholic church. In the early church, especially in the 3rd–5th century, it was a title of affectionate respect for any bishop. It is still used for the Eastern Orthodox patriarch of Alexandria and for Orthodox priests, but around the 9th century it came to be reserved in the West exclusively for the bishop of Rome. Catholic doctrine regards the pope as the successor of St. Peter the Apostle and accords him supreme jurisdiction over the church in matters of faith and morals, as well as in church discipline and government. Papal infallibility in matters of doctrine was asserted by the First Vatican Council in 1870. See alsopapacy, Roman Catholicism.