Gregory XII in the context of Council of Pisa

Peter of Candia, also known as Peter Phillarges (Greek: Πέτρος Φιλάργης) (c. 1339 – 3 May 1410), denominated Alexander V (Latin: Alexander PP.V; Italian: Alessandro V), was an antipope elected by the Council of Pisa during the Western Schism (1378–1417). He invalidly reigned briefly from 26 June 1409 to his death in 1410, in opposition to the true Roman Pope Gregory XII and the Avignon antipope Benedict XIII. In the 20th century, the Catholic Church reinterpreted the Western Schism by recognising the Roman Popes of the period as legitimate. The pontificate of Gregory XII was thus recognized to extend to 1415, and Alexander V was and is now recognized as an antipope.

Baldassarre Cossa (died 22 December 1419) was Pisan antipope as John XXIII (1410–1415) during the Western Schism. The Catholic Church today regards him as an antipope in opposition to Pope Gregory XII, whom it recognizes as the rightful successor of Saint Peter. John XXIII was also an opponent of Benedict XIII, who was recognized by the French clergy and monarchy as the legitimate pope.

Historically, the Annuario Pontificio recognized John XXIII the legitimate successor of Saint Peter. However, the Western Schism was reinterpreted in 1958 when Pope John XXIII chose to reuse the ordinal XXIII, which is now reflected in modern editions of the Annuario Pontificio. John XXIII is now considered to be an antipope and Gregory XII's reign is recognized to have extended until 1415.