Bishop of Velletri; antipope, 1058-1059; born Rome, Italy. He was elected in opposition to Pope Nicholas II by a faction of the Roman nobility after the death of Stephen (IX) X, who had commanded before he died that no election should take place until Hildebrand returned from Germany. John was enthroned by an illiterate priest but was deposed by Hildebrand and condemned by the Council of Sutri, 1059. He fled to Passarano, submitted to Nicholas II, 1060, and was publicly degraded in his presence by Hildebrand.