Regnal Names

Regnal Name: A regnal name, regnant name, or reign name is the name used by monarchs and popes during their reigns and subsequently, historically. Since ancient times, some monarchs have chosen to use a different name from their original name when they accede to the monarchy.

Ancient rulers in many parts of the world took regnal names or throne names which were different from their personal name. This is known to be true, for instance, of several kings of Assyria, and appears to be the case for several kings of Judah. In Ancient Egypt, Pharaohs took a number of names—the praenomen being the most commonly used, on occasion in conjunction with their personal name.

Immediately after a new pope is elected, and accepts the election, he is asked by the Dean of the College of Cardinals, "By what name shall you be called?" The new pope chooses the name by which he will be known. The senior Cardinal Deacon, or Cardinal Protodeacon, then appears on the balcony of Saint Peter's Basilica to proclaim the new Pope, informing the world of the man elected Pope, and under which name he would be known during his reign.

- wikipedia