- Actor Allusion: Juan berates his son, asking him why he named him Napoleon even though he completely lacks imagination. Rod Steiger himself played Napoleon just a year before.
- California Doubling: Parts of Almería and Grenada stand in for Mexico. Averted with the flashback scenes, which were filmed in and around Dublin (specifically Howth Castle and Toner's Pub).
- Completely Different Title:
- Duck, You Sucker! (Italy).
- Once Upon A Time...the Revolution (Some European releases).
- The Heroes of Mesa Verde (Latin America).
- Executive Meddling: Rod Steiger's casting was MGM's idea and didn't sit well with Sergio Leone, who wanted Eli Wallach (which caused Wallach to threatened to sue Leone, ending their friendship). It didn't help that Leone and Steiger didn't get along during the shoot, forcing James Coburn to mediate. Like most Leone films, the movie was significantly shortened in its international release, with heavy trims to its violence and political content: from 155 minutes to 138 for America, and to just 121 minutes in the UK.note It was also retitled A Fistful of Dynamite to capitalize on Leone's earlier movies.
- Fake Irish: James Coburn as John Mallory.
- Fake Nationality:
- Juan Miranda (Mexican of mixed Hispanic and Aztec ancestry) is played by American Rod Steiger.
- Mexican Colonel Reza is portrayed by French actor Antoine Saint John (though his first name of Günther suggests some German ancestry on Reza's part). Most of the other Mexican characters are played by either Italian or Spanish actors.
- Hostility on the Set: Sergio Leone and Rod Steiger did not get along, and Steiger even walked off the set. At one point their relationship grew so bad that Steiger refused to talk to Leone except through an intermediary (usually an assistant director or James Coburn), and even that didn't diffuse the tension.
- Missing Episode: There were entire scenes deleted from the film, such as a scene where Juan forces John to walk through the desert, in a similar manner to Tuco's torture of Blondie in The Good, the Bad and the Ugly. There are also surviving stills of a deleted scene showing Dr. Villega tortured by Gunther Reza's soldiers.
- Playing Against Type: Romolo Valli, most recognizable for comic relief roles in films like The Leopard, playing the tragic revolutionary Villega.
- Recycled Set: Some of the locations used previously featured in Leone's Dollar Trilogy films; for example, the Almería Railway Station, used for the train sequence in For a Few Dollars More, returns in this film as Mesa Verde's station.
- Wag the Director: Narrowly averted. Sergio Leone initially planned only to produce, asking Peter Bogdanovich to direct. Bogdanovich was heavily involved in the movie's preproduction, but realized Leone would be exercising creative control and backed out. Afterwards, Leone asked Giancarlo Santi, who had served as an assistant director on The Good, the Bad and the Ugly and Once Upon a Time in the West, to direct instead. After the first day of shooting, however, both Rod Steiger and James Coburn realized that Leone was pulling the strings and demanded that he direct instead, with Santi reduced to second unit work.
- What Could Have Been:
- The earliest draft of Sergio Donati's screenplay was a biopic of Pancho Villa. When this idea didn't pan out, Donati combined elements of this draft with another spec script called Mexico which eventually turned into the finished movie.
- The movie originally began with Animated Credits Opening showing a peasant plowing his field, with the camera finding a long white thread that turns out to be a fuse. An off-screen figure would say the title, then push a detonator which destroys the surrounding countryside. At the end, the peasant emerges from the rubble, shrugs, and resumes plowing. Though this featured in the final shooting script, it was never animated.
- The role of John Mallory was written for Jason Robards, who had played Cheyenne in Once Upon a Time in the West. However, the studio wanted a bigger name for his character.
- Leone offered Clint Eastwood the role of John Mallory, but he saw it as just a different take of the same character he had already played in the Dollars Trilogy, and he also wanted to end his association with the Italian film industry. As a result, he declined the offer and starred in Hang 'Em High instead.
- Malcolm McDowell was considered for both John Mallory and Nolan, but he was busy filming O Lucky Man.
- George Lazenby was originally chosen to play the lead role in this film and accepted, but he ultimately declined the role.
- According to Sergio Leone, Sam Peckinpah agreed to direct this film after Peter Bogdanovich had turned the project down, but for financial reasons he was turned down by United Artists. Leone's collaborators (especially writers Sergio Donati and Luciano Vincenzoni), noting the director's frequent embellishment of the facts concerning his films, claim that Peckinpah did not even consider it—Donati claimed Peckinpah was "too shrewd to be produced by a fellow director".
- And of course, the role of Juan was written for Eli Wallach. Wallach was enthusiastic to work with Leone again and turned down his current project for the chance, but United Artists wanted a bankable star, so they got Rod Steiger. Some foreign dubbing companies caught wind of this during the release of 'Don't Turn the Other Cheek' and had the same foreign actors voice both Steiger's Juan and Wallach's Max.
- Working Title: Mexico, Once Upon A Time...the Revolution.
Trivia / A Fistful of Dynamite