The leader of the Roman Catholic faith has often been quite nefarious.
Youngest Pope (Benedict IX)
Lady Pope (Joan I)
Last Honest Pope (Liberius)
Liberius was the last pope to publicly acknowledge the possibility that Jesus had been a man and not a god. As a consequence he is the only pope of the first 49 to have not been made a saint.
Last Murdered Pope (John Paul I)
Most Corrupt (Alexander VI)
Lots to choose from here but Alexander VI was the Borgia pope. Borgia bought the office, according to tradition, by bribing the cardinals with four mule loads of silver. His reign was rife with orgies, bribery, poisoning, judicial murder and extortion. He kept a stable of mistresses and fathered several children upon whom he bestowed lucrative papal offices. Alexander liked to keep score during orgies and rewarded cardinals who could ejaculate most often.
Most Debauched (Paul III & John XII)
John XII, like many popes, held bi-sexual orgies in the sacred palace which included having sex on the tombs of Saint Peter and Saint Paul. He appointed a ten year-old boy a bishop and took the child as his lover. John raped his sisters and nieces. Pope John XII was killed by the husband of one of his lovers.