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)
Caesar is a title of imperial character. It derives from the cognomen of the Roman dictator Julius Caesar. The change from being a surname to a title used by the Roman emperors can be traced to AD 68, following the fall of the Julio-Claudian dynasty. When used on its own, the title denoted heirs apparent, which would later adopt the title Augustus on accession. The title remained an essential part of the style of the emperors, and became the word for "emperor" in some languages, such as German (kaiser) and Russian (tsar).
Sculpture depiction of Julius Caesar
The Roman emperor Constantine the Great, mosaic in Hagia Sophia, Constantinople
Mehmed II and Ecumenical Patriarch of Constantinople Gennadios.