Papal Electors
Every Cardinal of the Roman Catholic Church is still called a Prince of the Church because their College of Cardinals elects a new pope (de facto from their number) during a period sede vacante in a special session called a conclave, where an age-limit applies. The Cardinals thus are an ecclesiastical equivalent to the Prince-electors of the former Holy Roman Empire, the other major elective monarchy in history.
Read more about this topic: Prince Of The Church