Maureen O'Hara was the first choice for Honey Bear Kelly, but MGM needed Ava Gardner in a movie and made John Ford cast Gardner instead, which is one of the reasons for Ford's vicious treatment towards Gardner while filming.
Clark Gable and Grace Kelly began an affair on the set that lasted for several months. After filming had ended, they resumed the affair while Kelly was filming The Country Girl (1954). Despite this story, Kelly biographer James Spada insists that although Kelly was infatuated with Gable, he did not want to get involved with a woman thirty years his junior. Although he liked her, Spada claims, theirs was a father-daughter relationship. However, Donald Sinden has said that Gable and Kelly did have an affair during filming.
Clark Gable did not get along with director John Ford during filming, and at one point walked off the set in protest at Ford's treatment of Ava Gardner. Ford also made several remarks about Gable's age and weathered appearance.
The censors in Spain did not allow adultery to be shown on the screen. For that reason, MGM changed the relationship of the characters of Linda Nordley (Grace Kelly) and Donald Nordley (Donald Sinden) from wife and husband to sister and brother in the dubbed version released in Spain. However, they did not delete a scene in which both share a bed together.
Donald Sinden (and all male members of the crew who removed their shirts) had to shave any hair from their chests daily, as Clark Gable (who did not have a hairy chest) thought it an affront to his 'manliness'.
The lead role was originally intended for Stewart Granger but MGM decided to employ Clark Gable instead. Production chief Dore Schary suggested to Granger that the film would entail a long filming separation from his wife Jean Simmons though Granger wanted to make the film regardless and later spoke disparagingly about Gable in his memoirs.
Although the original trailer for the film explains that "Mogambo" means "the Greatest," in fact, the word "Mogambo" has no meaning at all. Producer Sam Zimbalist came up with the title by altering the name of the Mocambo, a famous Hollywood nightclub.