Pope is the faction leader of the Papal States, which lies in Italy. He usually controls two provinces, the Papal States and Rome. But you might want to know that assasinating the pope isn't easy, and you should have a real high valoured assasin if you want to give it a try. (I haven't tried to assasinate the pope, but i guess he's just like any other faction leader.)
BTW, I'm just curious, how many of you folks has ever tried (and succeeded) to assasinate the pope? What was the valour of your assasin? Is assasinating the best way to get rid of the pope, I think I read somehere that a grand inquisitor actually suits that job better..