Callixtus (III) (flourished 12th century) was an antipope from 1168 to 1178, who reigned with the support of the Holy Roman emperor Frederick I Barbarossa.
Callixtus was elected antipope as Paschal III’s successor, in opposition to Pope Alexander III. He was Frederick’s protégé until the Treaty of Anagni (1176), which ended the schism in Alexander’s favour with the proviso that Callixtus should have an abbacy to compensate for his deposition. Callixtus ignored the treaty and remained obstinate even after the conclusion of the Peace of Venice (1177) between Frederick and the Lombards. In August 1178, however, he submitted to Alexander, who treated him generously, making him governor of papal Benevento.