Commissar is an English language transliteration of an official title (Russian: комисса́р) used in the Soviet Union and Russia from the time of Peter the Great.
The title was used during the Provisional Government for regional heads of administration, but it is mostly associated with a number of Cheka and military functions in Bolshevik and Soviet government military forces during the Russian Civil War (the White Army widely used the collective term "bolsheviks and commissars" for their opponents) and with the later terms People's Commissar (or narkom) for government ministers and political commissar in the military.
It is based on similar titles in a variety of languages (such as commissaire in French, Kommissar in German) most often attached to a criminal investigator in the police; they are usually translated as "commissioner".
Read more about Commissar: Other Uses