The Tsardom of Russia, also known as the Tsardom of Muscovy, was the centralized Russian state from the assumption of the title of tsar by Ivan IV in 1547 until the foundation of the Russian Empire by Peter the Great in 1721.
Moscovia, Herberstein, 1549
Russia, Mercator, 1595
Russia seu Moscovia, Mercator, Atlas Cosmographicae, 1596
Russia vulgo Moscovia, Atlas Maior, 1645
Tsar was a title used by Slavic monarchs. 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 —but was usually considered by Western Europeans to be equivalent to "king". It lends its name to a system of government, tsarist autocracy or tsarism.
Simeon I of Bulgaria, the first Bulgarian tsar and the first person who bore the title "tsar"
Reception of the Tsar of Russia in the Moscow Kremlin, by Ivan Makarov
Crowning of Stefan Dušan, Emperor of the Serbs, as tsar, by Paja Jovanović
Mostich's epitaph uses the title tsar (outlined): "Here lies Mostich who was ichirgu-boil during the reigns of Tsar Simeon and Tsar Peter. At the age of eighty he forsook the rank of ichirgu boila and all of his possessions and became a monk. And so ended his life." (Museum of Preslav)