Antipope John XXIII

Baldassarre Cossa (died November 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.

Cossa was born in the Kingdom of Naples. In 1403, he served as a papal legate in Romagna. He participated in the Council of Pisa in 1408, which sought to end the Western Schism with the election of a third alternative pope. In 1410, he succeeded Antipope Alexander V, taking the name John XXIII. At the instigation of King Sigismund of Germany, John XXIII called the Council of Constance of 1413, which deposed both John XXIII and Benedict XIII, accepted Gregory XII's resignation, and elected Pope Martin V to replace them, thus ending the schism. John XXIII was tried for various crimes, though later accounts question the veracity of those accusations. Towards the end of his life, Cossa restored his relationship with the Church and was made Cardinal Bishop of Frascati by Pope Martin V.

Education: University of Bologna

Source: Wikipedia — https://en.wikipedia.org/wiki/Antipope_John_XXIII