Mercurius, a Roman priest, was elected Pope John II; he was apparently the first pope to adopt a new name upon elevation to the papacy.

Pope John II, born Mercurius, was the Bishop of Rome from 2 January 533 to his death on 8 May 535. As a priest at St. Clement's Basilica, he endowed that church with gifts and commissioned stone carvings for it. Mercurius became the first pope to adopt a new papal name upon his elevation to the office. During his pontificate, John II notably removed Bishop Contumeliosus of Riez from his office, convened a council on the readmission of Arian clergy, and approved an edict of emperor Justinian, promulgating doctrine opposed by his predecessor, Pope Hormisdas.

A papal name or pontifical name is the regnal name taken by a pope. Both the head of the Catholic Church, usually known as the pope, and the pope of the Coptic Orthodox Church of Alexandria choose papal names. As of 2025, Leo XIV is the Catholic pope, and Tawadros II or Theodoros II is the Coptic pope. This article discusses and lists the names of Catholic popes; another article has a list of Coptic Orthodox popes of Alexandria.