Mister Iks or Mister X is a Russian musical comedy film in black and white, directed by Yuli Khmelnitsky. It is based on the Leningrad Theatre of Musical Comedy operetta of the same name from 1956. The operetta itself was a Russian adaptation of Emmerich Kálmán's Die Zirkusprinzessin. Filming began in 1957, with many of the actors and artists from the Leningrad Theatre working on the film. It premiered in the Soviet Union and other countries on May 2, 1958.