Antipope Felix V was first elected in opposition to this Pope. With the support of Filippo Maria Visconti, who was furious at this Pope's anti-Milanese policies, this Pope was expelled from Rome by the Colonna family but was able to re-conquer the Papal States by employing the condottiero Francesco Sforza. This Pope dissolved the Council of Basel in order to weaken the councilor movement, and he entrusted many important tasks to his powerful legate, Cardinal Julian Cesarini. This pope's crusade 
Antipope Felix V was first elected in opposition to this Pope. With the support of Filippo Maria Visconti, who was furious at this Pope's anti-Milanese policies, this Pope was expelled from Rome by the Colonna family but was able to re-conquer the Papal States by employing the condottiero Francesco Sforza. This Pope dissolved the Council of Basel in order to weaken the councilor movement, and he entrusted many important tasks to his powerful legate, Cardinal Julian Cesarini. This pope's crusade against the Ottoman Empire resulted in the death of King Wladyslaw II of Poland and the defeat of Janos Hunyadi at the Battle of Varna. To achieve his greatest goal, this Pope attended the Council of Florence-Ferrara, but the agreement signed there was scuttled due to public outrage in Constantinople. For 10 points, name this second post-Great Schism Pope, the successor of Martin V who presided over the failed attempt to unify the Catholic and Orthodox churches.
Antipope Felix V was first elected in opposition to this Pope.
Eugene IV [or Gabriele Condulmer; prompt on Eugene]