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.
