A Venetian of noble birth, little else is known about Angelo Corrarrio before he was made Bishop of Castello in 1380. Ten years later he was named Titular Patriarch of Constantinople, not to be confused with the Eastern Orthodox patriarch of the same title. In 1405, Pope Innocent VII gave Angelo a snazzy red hat and named him Cardinal-Priest of San Marco in Rome. 

A mere fourteen cardinals took part in the conclave that elected Pope Gregory XII. With the Western Schism -- a decades-old spat between France and the rest of Europe over who was the real pope -- still in full swing, Gregory wanted to bring unity to the Church above all else. He notified the papal poser in Avignon, Benedict XIII, of this desire, and the pair initially agreed to meet. It turned out that Benedict had no real desire to give up his title, and, after some unfortunate persuasion by ambitious family members, neither did Gregory.

About half of Benedict and Gregory's respective stables of cardinals quickly became disillusioned as a result. In a rather unprecedented move, the group gathered in Pisa and convened a general council -- or so they called it -- in order to depose both popes and elect a new one. Despite it being a canonical joke, the council was surprisingly well-attended, with over 500 bishops (or their proxies) present. After several months, the meeting resulted in the “election” of one Alexander V, technically an antipope. In 1410, Antipope John XXIII would succeed Alexander V. This went on for several more years until Gregory’s resignation (more on that in a minute) in 1415. He lived out his days in Ancona, a city on Italy’s eastern coast, before dying on October 18, 1417.

Remember the pinky promise all the cardinals made, where they vowed to stop at nothing to end the schism, even if it meant resigning from office? Well, Pope Gregory XII is remembered for being the man who made good on that oath, if only because so much nonsense had occurred by 1415 that he was probably ready for a vacation. 

Mercifully, King Sigismund of Rome convened the Church’s 15th ecumenical council, at Constance (Germany) in 1415. After the council had been operating for some time, Gregory, remembering his solemn vow from nearly 20 years prior, and sensing that only one option would truly bring union, sent legates to the council to first ratify the proceedings (since only a real pope can do that), then to read his letter of resignation. The Chair of Peter was vacated on July 4, 1415, and wouldn’t be filled for more than two years.

Fun Fact: Pope Gregory XII was technically the last pope to resign his office before Pope Emeritus Benedict XVI did so in 2013, a gap of 598 years. Benedict’s resignation, however, is still more akin to that of St. Celestine V (1294), given that neither of the two were doing so to end a massive rift in the Church. Interestingly enough, Benedict has outlived both Gregory and Celestine as a retired pontiff. The latter two lived no more than a couple years after abdicating, while Benedict has made it three and a half (and counting).