9. Elia Kazan
Although not born in America, Elia Kazan became a permanent resident when he was four years old and he made some of the defining American films of the 1950's so I don't have any problem putting him on this list. American cinema in the 1950's belonged to Kazan. In 1951, he introduced Marlon Brando to the world with the classic adaption of Tennessee William's play A Streetcar Named Desire. In 1954 he teamed up with Brando again with On the Waterfront which was not only one of the most acclaimed movies of the generation, but also one that was important given its subject matter and the volatile political climate at the time. In 1955 he discovered another young screen legend as he directed an adaption of John Steinbeck's East of Eden with James Dean playing the lead character. Those three films would probably be enough to secure his reputation but they only begin to show his impact on the film world. As one of the preeminent actor's directors in the world, Kazan was one of the most important figures in the explosion of Method Acting, not only did he help develop it, but he cast some of the first practitioners such as Marlon Brando in starring roles. He almost single-handedly discovered Brando and Dean, as well as Warren Beatty, Eve Marie Saint, and he helped mentor actors such as Dustin Hoffman, Al Pacino, and Robert De Niro. His focus on realism, both in terms of cinematic craft and social issues, have proved enormously influential and his unprecedented contributions to acting and a filmography full of classics, enable him to place so highly among America's greatest directors.