Dean Martin's agent approached Howard Hawks to consider his client for the role of the drunken deputy Dude. Hawks agreed to meet with Martin at 9:30 the next morning. When Hawks learned that Martin had done a show in Las Vegas until midnight, and hired a plane to fly him to the meeting, Hawks was so impressed that he simply sent Martin to get a costume and told him he had the part.
Malcolm Atterbury is listed in the credits (Jake, the stage driver), but like Harry Carey Jr., does not actually appear in the final cut of the movie.
John Wayne was nervous about the love scenes between his character and Feathers, since he was 51 and Angie Dickinson was only 26.
Ward Bond's death scene was filmed from a distance because it was actually a double. Bond had already left the set to be back on location for Wagon Train.
Montgomery Clift turned down the role of Dude, because he didn't want to work again with John Wayne and Walter Brennan.
Howard Hawks always wanted someone who would connect with teenagers to play Colorado. Reportedly, his first choice was Elvis Presley, who was enthusiastic about the opportunity. Unfortunately, Presley's manager, Col. Tom Parker, wanted too much money and top billing. Neither Hawks nor Wayne would have any of it, so the search continued.
Howard Hawks did not want to cast Ricky Nelson, whom he considered to be both too young and too lightweight, and deliberately gave him the fewest possible number of lines for a third-billed star. However, he later admitted that having Nelson's name on the poster had probably added $2 million to the film's box office performance.
Quentin Tarantino has said that before he enters into a relationship with a girl, he always shows her 'Rio Bravo' and if she doesn't like it, there is no relationship.
After seeing the film, Gary Cooper said it was "so phony, nobody believes in it." Ironically, Cooper had been a visitor to the set since he was filming The Hanging Tree nearby. "Rio Bravo" is considered to be John Wayne and Howard Hawks' reply to Gary Cooper's own film "High Noon" because neither Wayne or Hawks thought a real lawman would want or need to ask for help in handling a problem like Cooper's character did in that film.
Although Harry Carey Jr. was listed in the credits on-screen, he does not appear in the picture. Carey had a drinking problem at the time. He called director Howard Hawks "Howard" instead of "Mr. Hawks" on one of his first days on the set, infuriating Hawks. His contract, including his pay and his screen credit, was honored, but his part (a townsman) was cut.
At the Cowboy Hall of Fame in Oklahoma you can see the the rifle used by John Wayne (also used in El Dorado) and the hat and shotgun used by Walter Brennan.
Dude's nickname Borrachón is Spanish for "drunkard". In the Spanish dubbed version, the nickname was changed to Merluzón, meaning "big hake," so that Dude can explain the meaning of the nickname.
For most of the film Chance (John Wayne) has the front of his hat turned up to make him look a little soft and friendly. However in the tough guy scenes when Chance informs Nathan Burdette that he will have Stumpy kill his brother if there is any trouble, the front of the hat is turned down, in traditional tough guy mode.
For the first four full minutes of film (including credits) there is no dialog.
Hawks' instructions to Martin who showed up in an almost comical cowboy outfit on the first day of shooting, were not to play a cowboy but just play a drunk.
Inside joke: When Chance (John Wayne) wants to deputize Colorado he asks Stumpy (who is off camera) where he keeps the deputies' badges. While Chance is looking for the badges, Stumpy (Walter Brennan) still off camera tells him to look after his own props. Wayne started off in movie as a prop man and was known to get irate if the props were not where they were supposed to be.
More or less remade as El Dorado.
On May 8th, just one week into shooting 'Rio Bravo', Ricky Nelson celebrated his 18th birthday. As a gift, John Wayne and Dean Martin gave him a 300 lb. sack of steer manure, which they then threw Nelson into as a rite of passage.