Lev Kuleshov may well be the very first film theorist as he was a leader in Soviet montage theory — developing his theories of editing before those of Sergei Eisenstein (briefly a student of Kuleshov) and Vsevolod Pudovkin. For Kuleshov, the essence of the cinema was editing, the juxtaposition of one shot with another. To illustrate this principle, he created what has come to be known as the Kuleshov Effect. In this now-famous editing exercise, shots of an actor were intercut with various meaningful images (a casket, a bowl of soup, and so on) in order to show how editing changes viewers' interpretations of images.
In addition to his theoretical work, Kuleshov was an active director of feature-length films until 1943. Since 1943 Kuleshov was serving as the academic rector of Gerasimov Institute of Cinematography.