Tsar or czar (Russian: царь , Bulgarian, Serbian: цар, in scientific transliteration respectively car' and car), occasionally spelled csar or tzar in English, is a Slavonic term designating certain monarchs.
Originally, the title tsar (derived from Caesar) meant Emperor in the European medieval sense of the term, that is, a ruler who has the same rank as a Roman or Byzantine emperor (or, according to Byzantine ideology, the most elevated position adjacent to the one held by the Byzantine monarch) due to recognition by another emperor or a supreme ecclesiastical official (the Pope or the Ecumenical Patriarch).
Occasionally, the word could be used to designate other, non-Christian, supreme rulers. In Russia and Bulgaria the imperial connotations of the term were blurred with time and, by the 19th century, it had come to be viewed as an equivalent of King.
