John XXIII (Antipope)
John XXIII (b. about 1370; d. 22 November 1419) was Antipope of the Pisan party (1400–15). Cardinal Baldassare Cossa was one of the seven cardinals who in May, 1408, deserted Gregory XII, and, with those belonging to the obedience of Benedict XIII , convened the Council of Pisa, of which Cossa became the leader.
Descended from a noble but impoverished Neapolitan family, he embraced in his youth a military career, but later forsook it for the service of the Church. Endowed with great energy and very talented, he studied law at Bologna, where he took his doctor's degree, and then entered the service of the papal curia. On 27 February 1402, Boniface IX made him Cardinal-Deacon of St. Eustachius, and in the following year appointed him legate of Romandiola. On 17 March 1403, he set out for Bologna, where, until 1408, he proved himself an astute financial administrator of the papal territory, as well as a skilful statesman and able commander. At the same time he was utterly worldly-minded, ambitious, crafty, unscrupulous, and immoral, a good soldier but no churchman. He played an important part in the Council of Pisa (1409), and, when the two popes, Gregory XII of Rome and Benedict XIII of Avignon, were deposed, he conducted the election of Pietro Philarghi, who was elevate to the papacy and crowned as Alexander V. The new pope was entirely under the influence of Baldassare Cossa. The latter supported Louis of Anjou in a military expedition against Ladislaus of Naples. Louis seized on several fortresses in the Ecclesiastical States, and in 1400 captured Rome. Alexander V was now proclaimed pope at Rome, but refused to leave Bologna, where he died on 3 May 1410. In the hope of procuring an understanding with that pope, Prince Malatesta of Rimini, protector of Gregory XII, begged the cardinals of the Pisan obedience to defer a new election. These cardinals assembled at Bologna would not consent, but, supported by Louis of Anjou and the city of Florence, elected Baldassare Cossa, 17 May 1410. On 24 May Cossa was ordained priest, and on the following day was consecrated and crowned pope, taking the name of John XXIII.