Emperors

thumb|Emperor Naruhito and [[Empress Masako of Japan. The Emperor and Empress of Japan are the only current monarchs in the world left carrying this title.]]

thumb|Simeon I of Bulgaria, the first Bulgarian tsar and the first person who bore the title "tsar", by [[Alphonse Mucha|alt=Alphonse Mucha's The Slav Epic cycle No.4: Tsar Simeon I of Bulgaria (1923)]] thumb|Reception of the Tsar of Russia in the Moscow Kremlin, by [[Ivan Makarov]] thumb|Crowning of Stefan Dušan, [[Emperor of the Serbs, as tsar, by Paja Jovanović]]

founder of the Afghan Durrani Empire (r. 1747–1772)

The Tetrarchy was the system instituted by Roman emperor Diocletian to govern the ancient Roman Empire by dividing it between two emperors, the augusti, and their junior colleagues and designated successors, the caesares. It was kept in place between AD 293 and 324.

ruling title used by certain historical monarchs

legendary Scandinavian king

thumb|Signature of King-Emperor George V, King of the United Kingdom and the British [[Dominions, and Emperor of India (1910–1936).The 'R' and 'I' after his name indicate 'King' and 'Emperor' in Latin ('Rex' and 'Imperator').]]

Council of Carnuntum