The Danza: Several of the minor characters—Jo Ann Brody as Jo Ann (Augustine's mistress), Rutanya Alda as Rutanya (one of Marlowe's hippie neighbors), Jack Riley as Riley (the piano player), Pepe Callahan as Pepe (Augustine's bilingual thug).
Stillborn Franchise: Elliott Gould has said that so long as he is physically able he holds out hopes that he could reprise the role of Phillip Marlowe. He has a screenplay entitled It's Always Now, based on a Raymond Chandler story, The Curtain. The Chandler estate sold him the rights to the story for $1.
Elliott Gould ad-libbed many of Marlowe's quips. The shot of the two amorously-engaged dogs on the street of the Mexican village obviously wasn't planned but was memorable enough to stay in the film. He also improvised the scene in police custody in which he smears fingerprint ink all over his face.
Gould and Sterling Hayden's dialogue during the drinking scenes was improvised because Hayden was drunk and stoned on marijuana most of the time.
Altman originally wanted Dan Blocker (TV's Hoss Cartwright) whom he originally directed in early episodes of Bonanza to play Roger Wade. Tragically Blocker died from a post-surgery complication at the age of 44. The film is dedicated to him. John Huston was considered for Wade before Hayden was cast.
During filming of M*A*S*H, Elliot Gould and Donald Sutherland approached Fox executives about removing Robert Altman from the project, but decided not to go through with it. Gould admitted to Altman that he and Sutherland almost had him removed from the filming, but Donald Sutherland never told Altman about it. Subsequently, Altman never made another movie with Donald Sutherland.