"One Flew Over the Cuckoo's Nest", adapted from Ken Kesey's 1962 novel, dealt with life inside an OR mental institution.
His other notable films include "Hair" (1979), "Ragtime" (1981) and "Valmont" (1989).
"No matter what subject or genre he tackles, Miloš finds the universality of the human experience in every story, allowing us - his rapt audience - to recognize ourselves within the struggle for free expression and self-determination that Miloš so aptly portrays on the silver screen", past DGA President Taylor Hackford said at the time.
Born on Feb 18, 1932 in the Czech town of Caslav, Forman lost both parents in Nazi concentration camps.
His first feature in the USA, 1971's Taking Off, was a critical if not commercial success.
His first American film was "Taking Off" in 1971 and he followed it up with "One Flew Over the Cuckoo's Nest" in 1975, which became the second film to win five Oscars picture, director, actor, actress and adapted screenplay.
The film starred Nicholson as a man battling the system in a psychiatric establishment and was based on Ken Kesey's novel.
"Milos loved life. I will miss his laughter".
"The Communist Party was my Nurse Ratched, telling me what I could and could not do".
Writer and producer Larry Karaszewski, who made Man On The Moon and The People vs Larry Flynt with Forman, wrote: "Milos Forman was our friend and our teacher". Its Oscars included best picture and best director. "He passed away quietly, surrounded by his family and his closest people", she said.
Milos is survived by wife Martina and four sons - twins Matej and Petr Forman from the second marriage and Andrew and James, named after Andy Kaufman and Jim Carrey, from the third marriage.