The term 'Russian EMPEROR' is used to refer to the rulers of the Russian Empire, and is often used interchangeably with the terms CZAR, TSAR, and Tzar. CZAR, TSAR, and Tzar are all four-letter words that refer to the same position, and are derived from the Latin word Caesar, meaning 'EMPEROR'. The title of CZAR was first used by Ivan III in 1472, and was used until the Russian Revolution in 1917. TSAR was the title used by Peter the Great in 1721, and was used until the Russian Revolution. Tzar was a variant of TSAR, and was used in some parts of the Russian Empire.