The term Tsar is mainly used to mean the emperor of Russia but can also refer to a ruler of several Slavic kingdoms. The term is a Latinization of the Russian word ‘czar’, which is ultimately derived from the Latin ‘Caesar’.
In Russia, Ivan IV Vasilyevich, also known as the Terrible, became the first Tsar of All the Russias in 1547. He died from a stroke while playing chess with Bogdan Belsky in 1584.
However, in history, there have been many more Tsars and Tsardoms. In fact, the title Tsar has been used as the official title of the supreme ruler in the following states:
- First Bulgarian Empire (913–1018)
- Second Bulgarian Empire (1185–1422)
- Serbian Empire (1346–1371)
- Tsardom of Russia (1547–1721)
- Tsardom of Bulgaria (1908–1946)
Knowledge Guild 
And Kaiser also means Caesar! From the HRE on, people were always trying to hold on to some continuity to the good old days of Ancient Rome.