I. A saint and pope of the Roman church, according to some, the second after St. Peter, and a martyr under Domitian in 91; according to others, martyred about 109, having succeeded Clement I. as the fifth bishop of Rome.

II. An anti-pope, whose original name was Peter de Leon. He was said to be of Jewish descent, was born in Italy, and educated at the university of Paris. He entered the order of Cluny, and was afterward cardinal and legate of Pope Calixtus II. both in England and France. He was elected pope in 1130 by a portion of the cardinals in opposition to Innocent II., and was sustained by the Romans, Milanese, and Sicilians. In spite of the arms of the emperor Lothaire and the opposition of other sovereigns and of the clergy generally, Anacletus maintained himself at Rome till his death, Jan. 7, 1138.