Out of the 266 Popes to have ruled the Catholic Church, ten in particular stand out for their wickedness. This is a list of the ten with a description of their errors and faults.
1. Liberius, reigned 352-66 [Catholic Encyclopaedia]
Pope Liberius is the first Pope not to be canonised a saint. He reigned during the height of the Arian crisis during which a large majority of the Church believed that Jesus was not God, but merely a man.