Tsar is the title for the supreme ruler of Bulgaria in 913–1422, later usage in 1908–1946, the supreme ruler of Serbia in 1346—1371 and the emperor of Russia from 1546 until 1721. Since 1721 the title of Russian emperors was imperator, but the word tsar remained in common use until the Russian Revolution in 1917.
Tsar is also spelled tzar, czar, and csar. It is the Eastern European word for caesar, and can be translated to emperor. The system of government used during the Tsardom of Russia and the Russian Empire was called Tsarist autocracy, also known as Tsarism.
The last tsar to rule Serbia was Stephen Uroš V.
The last tsar to Rule Russia was Nicholas II.
The last tsar to Rule Bulgaria was Boris III.