John XIII, pope of the Catholic Church (born 930)

Pope John XIII was the bishop of Rome and ruler of the Papal States from 1 October 965 to his death. His pontificate was caught up in the continuing conflict between the Holy Roman emperor, Otto I, and the Roman nobility. After long and arduous negotiations, he succeeded in arranging a Byzantine marriage for Otto II, in an effort to legitimize the Ottonian claim to imperial dignity. He also established church hierarchy in Poland and Bohemia.

The Catholic Church, also known as the Roman Catholic Church, is the largest Christian church, with 1.27 to 1.41 billion baptized Catholics worldwide as of 2025. It is among the world's oldest and largest international institutions and has played a prominent role in the history and development of Western civilization. The Church consists of 24 sui iuris (autonomous) churches, including the Latin Church and 23 Eastern Catholic Churches, which comprise almost 3,500 dioceses and eparchies around the world, each overseen by one or more bishops. The pope, who is the bishop of Rome, is the chief pastor of the church.