In that spirit, here are my picks, which will clearly differ from SCREEN RANT (and probably most others).
In American noir, we must include Bogart, Garfield and Ryan for the actors--these three are indisputable.
For the actresses, we must include Stanwyck, Crawford and Grahame off the top.
We'd also need to add Dan Duryea, and I think we'd be remiss if we didn't put Edward G. Robinson into the mix as well.
For the sixth American actor, it becomes a tossup between Dana Andrews and Robert Mitchum.
On the outside looking in are two noir stalwarts who should at least be mentioned: Edmond O'Brien and Richard Conte.
For actresses "on the bubble," there's Liz Scott (I hear groaning from Chi-Bob's man-cave as I type this), Audrey Totter, Marie Windsor and Claire Trevor.
We then should move away from the US and bring in foreign actors, where we need to consider actors like Jean Gabin, Erich von Stroheim and Michel Simon from France, and Tatsuya Nakadai from Japan. Robert Hossein also deserves mention for his double duty as actor/director and for galvanizing the "last wave" of classic French noir.
The French actress with the most consistent track record in noir is Simone Signoret, but the actress in the most actual noirs is Ginette Leclerc, a vastly underrated performer.
That's more than twelve, of course, but it serves as a bit of a helping hand for those of you who will (hopefully) chime in, if only to vote for Alan Ladd and/or Veronica Lake, or Van Heflin, or...Tito Vuolo!