Scorsese became friends with the influential "movie brats" of the 1970s: Brian De Palma, Francis Ford Coppola, George Lucas and Steven Spielberg. It was De Palma who introduced Scorsese to Robert De Niro. During this period, Scorsese worked as the assistant director and one of the editors on the documentary "Woodstock" (1970) and met actor–director John Cassavetes, who became a close friend and mentor. In 1972, Scorsese made the Depression-era exploiter "Boxcar Bertha" for B-movie producer Roger Corman, who also helped directors such as Francis Ford Coppola, James Cameron, and John Sayles launch their careers. It was Corman who taught Scorsese that entertaining films could be shot with very little money or time, preparing the young director well for the challenges to come with "Mean Streets". Following the film's release, Cassavetes encouraged Scorsese to make the films that he wanted to make, rather than someone else's projects.