Antipope , a false claimant of the Holy See in opposition to a pontiff canonically elected. At various times in the history of the Church illegal pretenders to the Papal Chair have arisen, and frequently exercised pontifical functions in defiance of the true occupant. According to Hergenröther, the last antipope was Felix V (1439-49). The same authority enumerates twenty-nine in the following order:

Hippolytus (?), III century.
Novatian, 251.
Felix II, 355-365.
Ursicinus, 366-367.
Eulalius, 418-419.
Laurentius, 498-501.
Constantine II, 767.
Philip, VIII century.
Anastasius, 855.
Leo VIII, 956-963.
Boniface VII, 974.
John XVI, X century.
Gregory, 1012.
Sylvester III, 1044.
Benedict X, 1058.
Honorius II, 1061-72.
Guibert or Clement III, 1080-1100.
Theodoric, 1100.
Aleric, 1102.
Maginulf, 1105.
Burdin (Gregory VIII), 1118.
Anacletus II, 1130-38.
Victor IV, 1159-64.
Pascal III, 1164-68.
Calixtus III, 1168-77.
Innocent III, 1178-80.
Nicholas V, 1328-30.
Robert of Geneva (Clement VII), 20 September, 1378 to 16 September, 1394.
Amadeus of Savoy (Felix V), November, 1439 to April, 1449.

The Catholic Encyclopedia, Volume I, p. 582
Nihil Obstat, March 1, 1907. Remy Lafort, S.T.D., Censor
Imprimatur. +John Cardinal Farley, Archbishop of New York