In 1409 a grouping of Cardinals from both Avignon and Rome met at Pisa, started a Council, and deposed both existing popes to elect a third pope, "John XXIII". He proved to be a bit of a disappointment, and failed to muster any support of substance.
He resided in Bologna, and transferred to Rome once his supporters had taken the city from Gregory XII. However, John XXIII was persuaded to convene the Council of Constance, which deposed all three existing papal pretenders and elected Martin V as Pope. Thus was the Great Schism ended.
Note that John XXIII (confusingly numbered identically to the great Pope of the 20th Century, also John XXIII, who convened the famed Second Vatican Council) was the subject a great quote from Edward Gibbon in his epic Decline and Fall of the Roman Empire. In his book, Gibbon describes the deposition trial as follows: "The most scandalous charges were repressed; the vicar of Christ was only accused of piracy, rape, sodomy and incest." In spite of his deposition, this Pope is not considered an anti-pope, but is held to be the legitimate holder of the Papal throne from his election until the election of Martin V.