This movie is set in the 1940s but the Marlowe movie follow-up to this film, The Big Sleep (1978), was actually set in the 1970s, making Robert Mitchum's two Chandler pictures playing Phillip Marlowe discontinuous in their universes in time and thus separate entities.
Playing private eye Phillip Marlowe was actor Robert Mitchum who was well known for his roles in many film noir, detective and crime fiction movies from the 1940s including the classic Out of the Past (1947).
The dark pin-striped suit worn by Robert Mitchum in the film was the only one available from the wardrobe department, with no backup suit available if needed. Originally made for Victor Mature during the 1940s, Mitchum hated the outfit, and complained constantly during production about having to wear "Victor Mature's old farted-up suit."
When asked why Philip Marlowe (Robert Mitchum) cares about Moose Malloy (Jack O'Halloran), he says, "I don't know. Ever since I saw that movie, King Kong, I've been a sucker for any gorilla that falls in love with a girl." O'Halloran would appear in the King Kong remake, the following year.
Part of a 1970s revival cycle of film noir and hard-boiled detective movies which included such non-Chandler fare as Gumshoe (1971), Chinatown (1974), and The Black Bird (1975). Five Chandler filmed adaptations were made around this period including this cinema movie.
Robert Mitchum's interpretation and characterization of Raymond Chandler's Phillip Marlowe detective character was much older and world-weary than the earlier cinematic incarnations of the Marlowe private eye.