A "tsar" was a title used for the emperors of Russia, similar to the term "king" in other countries. The word comes from the Latin "Caesar," which was used to denote rulers in ancient Rome. Tsars ruled with absolute power and were often seen as the representatives of God on Earth. The most famous tsar is probably Peter the Great, who modernized Russia in the 18th century. The tsar's reign often included a strong central government and a focus on expanding the country's territory. The last tsar, Nicholas II, ruled until the Russian Revolution in 1917, which led to the end of the monarchy and the rise of the Soviet Union.