Baldassarre Cossa (c. 1370 – 22 December 1419) was Pisan antipope John XXIII (1410–1415) during the Western Schism. The Catholic Church regards him as an antipope, as he opposed Pope Gregory XII whom the Catholic Church now recognizes as the rightful successor of Saint Peter. He was also an opponent of Antipope Benedict XIII, who was recognized by the French clergy and monarchy as the legitimate Pontiff. 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 Sigismund, King of the Romans, Pope John called the Council of Constance of 1413, which deposed 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. Early life Baldassarre Cossa was born on the island of Procida in the Kingdom of Naples, the son of Giovanni Cossa, lord of Procida. Initially he followed a military career, taking part in the Angevin-Neapolitan war. His two brothers were sentenced to death for piracy by Ladislaus of Naples. He studied law at the University of Bologna and obtained doctorates in both civil and canon law. Probably at the prompting of his family, in 1392 he entered the service of Pope Boniface IX, first working in Bologna and then in Rome. (The Western Schism had begun in 1378, and there were two competing popes at the time, one in Avignon supported by France and Spain, and one in Rome, supported by most of Italy, Germany and England.) In 1386 he is listed as canon of the cathedral of Bologna. In 1396, he became archdeacon in Bologna. He became Cardinal deacon of Saint Eustachius in 1402 and Papal legate in Romagna in 1403. Johann Peter Kirsch describes Cossa as "utterly worldly-minded, ambitious, crafty, unscrupulous, and immoral, a good soldier but no churchman". At this time Cossa also had some links with local robber bands, which were often used to