Which Soviet director is known for his theory of the 'cinema-eye' and his experimental film 'Man with a Camera' (1929), which explored the possibilities of montage and the camera as a tool of observation?

Dziga Vertov was a Soviet documentary filmmaker and film theorist, known for his focus on 'kino-eye', which sought to capture reality without a script or actors. His film 'The Man with the Camera' is a milestone in documentary and avant-garde cinema, exploring the potential of the camera as an impartial eye.