Question: Which film director also appeared on screen as an actor, Dziga Vertov or Frederic Zelnik?
Related documents: [0]  [DOC] Frederic Zelnik (17 May 1885 - 29 November 1950) was one of the most important producers-directors of the German silent cinema. He also appeared on screen as an actor. [END] 
[1]  [DOC] Dziga Vertov (Russian: Дзига Вертов ; born David Abelevich Kaufman, Russian: Дави́д А́белевич Ка́уфман , and also known as Denis Kaufman; 2 January 1896 – 12 February 1954) was a Soviet pioneer documentary film and newsreel director, as well as a cinema theorist. His filming practices and theories influenced the cinéma vérité style of documentary movie-making and the Dziga Vertov Group, a radical film-making cooperative which was active from 1968 to 1972. [END] 
Answer: 
Frederic Zelnik
Frederic Zelnik