Tsar (Tzar, Czar, or Csar; Bulgarian, Serbian and Ukrainian: цар; Russian: царь ) is a title used to designate certain European Slavic monarchs or supreme rulers. As a system of government in the Tsardom of Russia and Russian Empire, it is known as Tsarist autocracy, or Tsarism. The term is derived from the Latin word Caesar, which was intended to mean "Emperor" in the European medieval sense of the term - a ruler with the same rank as a Roman emperor, holding it by the approval of another emperor or a supreme ecclesiastical official (the Pope or the Ecumenical Patriarch) - but was usually considered by western Europeans to be equivalent to king, or to be somewhat in between a royal and imperial rank.
Occasionally, the word could be used to designate other, secular, supreme rulers. In Russia and Bulgaria the imperial connotations of the term were blurred with time, due to the medieval translations of the Bible, and, by the 19th century, it had come to be viewed as an equivalent of King.
"Tsar" was the official title of the supreme and great ruler in the following states:
- First Bulgarian Empire, in 913–1018
- Second Bulgarian Empire, in 1185–1422
- Serbian Empire, in 1346–1371
- Tsardom of Russia, in 1547–1721 (replaced in 1721 by imperator, but remained in common usage until 1917)
- Tsardom of Bulgaria, in 1908–1946
The first ruler to adopt the title tsar was Simeon I of Bulgaria. Simeon Saxe-Coburg-Gotha, the last Tsar of Bulgaria, is the last person to have borne the title Tsar as well as being the last surviving person to do so.