The video game Ross Webster plays was created for the film. It originally looked so life-like that the creators were asked to make it look more computer-like.
After Margot Kidder expressed her disgust about the firing of Richard Donner to the producers, her role was cut to 12 lines, and less than 5 minutes of screen time.
Enid Saunders character, Minnie Bannister (in one of the Smallville sequences), is a very obscure in-joke by Richard Lester. He had a long association with the cast members of the BBC radio show "The Goon Show." Minnie Bannister, voiced by Spike Milligan, was a recurring character.
The original title was "Superman vs. Superman". The producers of Kramer vs. Kramer threatened a lawsuit, refusing to believe the Salkinds' explanation that it was intended as a play on various "Superman vs..." comic stories. Eventually Pierre Spengler suggested that "Superman III" would be a more sensible title anyway, and the issue was dropped.
Superman creates a diamond by squeezing a piece of coal in his hand, a reference to some earlier Superman comic book stories, where he performed the same action.
According to the writers, the original choice to play Ross Webster was Alan Alda. They wanted an actor who could be ruthless without losing any charm. Executive producer Ilya Salkind said in the DVD commentary that his choice was Frank Langella. Langella later starred as Perry White in Superman Returns.
When it was first revealed to producers that Lana Lang would be a single mother, a comic book was quickly written explaining how Lana came to be in that situation.
The little boy who appears waiting by the photo-booth while Clark Kent changes into Superman was actually the same little boy who played baby Kal-El (Superman) in Superman.
The first time Christopher Reeve had top billing in a Superman movie. In the first film, he was behind Marlon Brando and Gene Hackman; for the second he was behind Hackman.
According to Ilya Salkind, an earlier version of the script included the comic book villains Brainiac and Mr. Mxyzptlk teaming up, and Superman meeting his cousin, Supergirl, which would lead to the potential Supergirl spin-off.
According to the producers' commentary on the Superman III: Deluxe Edition DVD, this film was actually not a flop. While critics and fans generally expressed disappointment with the film, and its $60 million gross fell short of the previous two movies' $100 million+ gross, Superman III still made an impressive profit, despite stiff competition from Star Wars: Episode VI - Return of the Jedi (which opened 3 weeks earlier) and Octopussy (which opened 10 days earlier).
According to the Vulcan weather satellite, the chemical composition of Kryptonite (shown on Gus Gorman's computer) is: 15.08% Plutonium, 18.06% Tantalum, 27.71% Xenon, 24.02% Promethium, 10.62% Dialium, 3.94% Mercury, and 0.57% Unknown (Gorman replaced this with Tar).
A routine of Richard Pryor's, often included in "best of" CDs is a skit called "Super N****r" about a black Superman who is disguised a janitor working for the Daily Planet.
Frank Oz played a brain surgeon in a deleted scene from the montage of the supercomputer causing a nationwide power outage. It's included in the extended TV version of the film. He also worked on puppet sequences, which were also deleted, and not included in any version. The film's director of photography, Robert Paynter, previously shot An American Werewolf in London, in which Oz appeared, and would go on to shoot The Muppets Take Manhattan (Oz's directorial debut) and Little Shop of Horrors.
The tanker that leaks oil into the Atlantic is the British Reliance, owned by BP Amoco Shipping. It was built in 1975, flew the Bermudan flag, and was demolished in December 1999.
The trivia items below may give away important plot points.
Filmed in Calgary, Alberta, home of Canada's first Kentucky Fried Chicken franchise. It includes multiple KFC references: the Metropolis computer school payroll is handed out by a man in a Sanders-style goatee, Gus walks past a Smallville display with Kentucky Colonel outfits, Gus drags the intoxicated Brad past a closet whose open door shows a bag hanging full of KFC items, and Gus uses a "chicken in the bucket" recipe to explain to Ross why Kryptonite doesn't kill Superman.
Richard Pryor's character steals money from his company by collecting fractions of a cent from other accounts and collecting them in his personal account. In computer crime terminology, it's called the "salami technique."