In the UK, the executive is the cabinet and in times long gone a minister had the role of telling the monarch the proposed legislation in the House of Commons and other matters. This became very useful as the first of these PM's was the only minister in the cabinet who could speak German (the King at the time could not speak English!). In modern times however, although this term is still used, it in effect does not apply considering the vast powers of the Prime Minister.
This is not the view of the Roman Catholic Church, which considers the Pope to be Vicar of Christ, successor of Saint Peter, and superior to the rest of the bishops, successors of the Apostles.