I've taught a few Film Noir classes in the past and one of the toughest things to start with is just what is film noir and what movies qualify?
1941's STRANGER ON THE THIRD FLOOR certainly has a lot of the elements, so does THE MALTESE FALCON (also 1941) but I'd argue that REAL film noir must have certain elements:
1. Dark shadowy cinematography (the term Film Noir translates into Dark Film).
2. A Femme Fatale-- she's no good and usually leads the protagonist down a dark road.
3. A protagonist who is either equally dirty him (or her) self or makes a bad choice.
4. The film has to be American. The French coined the term in reference to post WWII American films they were watching.
5. The ending should be pessimistic or at the very least end on a dour note.
I'd even quantify by adding there has to be death involved, and there should be hot weather. Film noir's are dark and sweaty.
Using those qualifications Billy Wilder's 1944 film DOUBLE INDEMNITY becomes the first film noir. Perfect because our protagonist is none other than Fred MacMurray-- the guy who was the dad in MY THREE SONS, the professor in FLUBBER, and the physical basis for Captain Marvel. This guy is red white and blue white bread-- but in this movie he's lured by Barbara Stanwyck into a plan to murder her husband and collect the insurance money.