King, Emperor, Tsar and Caliph: A Guide to Titles

A king traditionally rules one kingdom or people, an emperor rules many, or claims succession from Rome. Tsar is the Slavic rendering of Caesar, used first by Ivan IV of Russia in 1547. Kaiser is the German form.

Sultan meant authority in Arabic, the title of Ottoman and Ayyubid rulers. Caliph claimed leadership of the whole Muslim community as successor to the prophet. Pharaoh, great house, was the ancient Egyptian royal title.

In modern Europe most surviving monarchs are simply kings or queens.