Raymond Chandler built his hardboiled detective hero, Phillip Marlowe, using this blueprint: “Down these mean streets a man must go who is not himself mean, who is neither tarnished nor afraid. He is the hero; he is everything. He must be a complete man and a common man and yet an unusual man. He must be, to use a rather weathered phrase, a man of honor—by instinct, by inevitability, without thought of it, and certainly without saying it. He must be the best man in his world and a good enough man for any world."
Robert Mitchum's Marlowe isn't Humphrey Bogart's ("The Big Sleep") Marlowe. It is its own thing, and as perfect in its own way as anyone could ask for.