Tim Daly said the reason he signed on to do Superman's voice in this series was because he thought it would be fun to play a superhero in a superhero cartoon. He later said he underestimated just how difficult voice acting for a superhero, especially one of Superman's stature, would be.
Lex Luthor's henchwoman, Mercy Graves, is a character originally created for the show. She was eventually added as a member of the cast in the comics. The comics version of Mercy has blonde hair and does not wear a chauffeur's uniform.
When Martha Kent first finds the baby Kal-El she suggests Christopher and Kirk as possible names for the child before settling on Clark, a reference to both Christopher Reeve and Kirk Alyn, who had both played previous incarnations of Superman on the screen.
This series was made to coincide with a new Superman film titled "Superman Lives" (originally titled "Superman Reborn"). However, the film would spend years in development hell and would be eventually released years later as Superman Returns (2006).
When developing this show, the crew was playing around with different ideas. According to Bruce Timm, at one point they said, "Well, what if we did Superman and the Justice League, where every episode would have Superman in it, plus two other members of the Justice League?" Timm sat down and did a bunch of different characters, even some that had never even been in the JLA, like the Question. They tried to put in as weird a mix as they could so it wasn't just Superman, Aquaman, Hawkman etc... Batman wasn't going to be part of it since he already had his own show. In the end, DC President and Editor-In-Chief Jenette Kahn put a stop to it. She thought it was not a good idea, since they were just reintroducing Superman to the audience, and she thought teaming him up with the JLA would be diminishing to him. Everyone all kind of agreed with that, so the JLA idea was dropped.
Mala is based on the Kryptonian Phantom Zone villains Faora and Ursa, but is named after a male Phantom Zone villain. Leslie Easterbrook was the original voice actress, but was replaced with Sarah Douglas, who also played Ursa in Superman (1978) and Superman II (1980).
Originally produce Bruce Timm was going to style this series after Max Fleischer's Superman (1941), but Timm decided to use a futuristic look to the series that the producers called "Ocean Liner Deco". The reason why they didn't make it Fleischer-esque is that Timm didn't want anybody to literally put it side-by-side with the old Fleischer shorts and say, 'They're just doing a third-rate knockoff of the Fleischers'. Alex Toth though the series should look like the Fleisher version and disagreed with this decision on the art. Because of this, Toth never spoke to Timm again.
The Superman design on this show is based on his familiar well known classic design with short hair. At the time the series was in development Superman's design was slightly revamped in the comics giving him longer hair and in 1997 he has given an extreme overhaul with new electric powers, completely new costume, and split in two beings as Blue and Red Superman. With the movie project going into development hell and the popularity of this series, Superman returned to his classic design in 1998.
The image of Superman used at the background during the end credits was supposed to be the promotional image for merchandising. However, it was thought that the image didn't really look like Superman and a different promotional image was used.
This series was originally meant to have an opening montage similar to the one Batman: The Animated Series (1992) had, showcasing what Superman could do in an awe inspiring manner, but the animators were unable to finish it by the deadline, so a montage featuring clips of Superman in action alongside his supporting cast from the episodes was utilized instead. Part of the abandoned montage, which featured Superman flying in the night sky of Metropolis, made it into the opening. Another such shot was the final one in the opening; the classic visual of Clark Kent ripping open his shirt to reveal the big red "S."
Sherman Howard auditioned for the role of Lex Luthor (a role he had played on Superboy (1988)). Clancy Brown, originally auditioned for the lead role of Superman / Clark Kent, but when Bruce Timm heard his audition, he immediately offered Brown the part of Luthor.
Though Lobo was virtually unchanged from his comic appearances, the character is, nevertheless, significantly different from his comic book roots, as his modus operandi has been simplified for younger audiences. Much like appearances by Carnage and the Punisher on FOX Kids' Spider-Man (1994) series, Lobo had to be toned down in terms of his activities, resulting in a character that alluded to excessive violence without perpetuating much of it on camera. Gone was the "kill 'em all" approach to bounty hunting, as well as his trademark metal hook (seen briefly on this series, but replaced by a crowbar in most scenes), as he took his targets alive rather than dead.
Adam Baldwin was considered for the role of Superman/Clark Kent but was not available, so the part went to Tim Daly instead. Nearly ten years later, Baldwin went on to play the role in the direct-to-DVD movie Superman/Doomsday (2007).
"Legacy" was intended to kick off a season's worth of episodes about Superman regaining the world's trust. However, a pushback and other projects (Batman Beyond (1999)) led to it being produced as the finale instead, while the theme of public distrust for metahumans became an underlying plot thread in Justice League (2001).
For adapting Supergirl, the creative team wanted a take on her that was not the artificial protoplasmic lifeform called Matrix from post-crisis continuity that takes the shape of Supergirl and later combined with Linda Danvers, a confused and angst-ridden human girl. Paul Dini and Bruce Timm originally wanted to use the original pre-crisis Kara Zor-El version of Supergirl, which is Superman's cousin from Krypton, however, they ran into a wall with DC because they insisted that Superman be the last Kryptonian. So they did a compromise: she's from a small planet called Argos in the neighboring system that was colonized by Kryptonians, but they've evolved slightly differently.
When adapting Darksied for this series the creative team was able to use elements of the Jack Kirby Mythos that worked on a more commercial aspect, reducing Darkseid's whole central being and mythos into something that's kind of easily palatable to the key audience. This version of the Anti-Life Equation is basically that Darkseid feeds on the despair of people, so that's why he wants Earth and that's why he wants to destroy Superman. He's going to come to Earth and take their greatest hero and reduce him to nothing. He's going to feed off the despair of the entire planet.
David Kaufman was chosen to voice Jimmy Olson. Coincidentally, in an episode of Back to the Future The Animated Series titled "Super Doc", Marty McFly (also voiced by Kaufman) goes by the name Jimmy Olsen while in 1952.
Brainiac's design on this series is an original design by producer Bruce Timm that kind of emulates Jack Kirby's art style. An additional change to the character for the series is the change in Brainiac's skin color, as Timm and the creative team exchanged the traditional green for turquoise. In the comics, Brainiac 13 was designed to resemble the animated Brainiac from this series.
Intergang, an organized crime gang armed with technology supplied by the villainous New Gods of the planet Apokolips, makes their animated debut for the first time in this series. The organization was initially run by Bruno Mannheim, but was reorganized later under the leadership of Granny Goodness.
This version of Brainiac, draws heavily from the Silver Age Brainiac-in that it is an artificial intelligence that wanders the cosmos searching for knowledge-but the Coluan back-story was scrapped in favor of a Kryptonian one, which better fit the needs of the animated series. By making this change, a parallel was created between Brainiac and the Eradicator-a Post-Crisis Kryptonian computer system that sought, at different times, to remake Earth into a new Krypton and to remake Kal-El into the ultimate Kryptonian. The Post-Crisis Brainiac, where he was re-imagined as Vril Dox and possessed the mind and body of circus mentalist Milton Fine, was completely ignored in the animated adaptation.
The Flash is the first DC super hero to make a guest appearance on this series. The producers didn't reveal The Flash's secret identity because they had not fully decided on which Flash they were going to use Wally West or Barry Allen. This was eventually settled on Justice League (2001) when it was revealed the Flash is indeed Wally West.
Livewire was an original villain created for this series. Originally, she was Leslie Willis, an obnoxious shock jock and notorious critic of Superman, who was transformed into the electric-powered supervillain.
In choosing villains from the Phantom Zone, it was decided to use Jax-Ur, the most frequent Phantom Zone villain in pre-crisis stories. This version of Jax-Ur was more like an amalgamation of General Zod who doesn't officially appear in the animated universe.
Luminous was an original villain for this series. Originally, he was a guy named Edward Lytener who Lois Lane spurned, but when he was brought back for a second appearance he was upgraded to supervillain scale and was given light hologram powers to be more of a physical threat to Superman.
In this series John Henry Irons is a designer for LexCorp who works to create a prototype suit of powered armor for the Metropolis SCU, but the suit's neural interface system had adverse psychological effects on its user Sgt. Corey Mills. Encouraged by Superman, Irons worked to perfect the suit with the help of his niece Natasha, becoming the superhero Steel.
The animated Steel does not feature the cape he adapted from Superman after he saved John's life in Superman: The Man of Steel #19, and lacks his 'S' shield (although he does wear a jersey with a 5 on the front, a possible homage). The change also coincide with the costume seen in the Steel (1997) film. In his premiere episode "Heavy Metal", his rivet guns were replaced with forearm-mounted lasers.
Maxima makes her official debut outside of the comics in this series. Her design keeps her original colors from the comics but is redesigned to have a Jack Kriby-type look. Her personality is a bit more whimsical and of her myriad powers, only her strength and durability remained, and she was also seen to be capable of metal manipulation.
Supergirl's costume was redesigned for this series which gave her an individual independent look rather than being really close to Superman's costume. The redesigned costume consisted of a white shirt and gloves with a blue skirt and red boots. This design was later transferred to the comics after the series ended.
This series introduced Kyle Rayner as Green Lantern for the first time outside of the comics. The animated Kyle Rayner retains his background as a struggling-but-gifted graphic artist, but for the Daily Planet instead of just freelance work. Rayner also had character elements of Hal Jordan by inheriting the ring from Abin Sur, who sent it off to Rayner with his dying breath and having clean cut brown hair and a small domino mask as opposed to the jet black hair and larger mask Rayner had in the comics.
Argo, Krypton's "sister planet" where Supergirl comes from, is actually gets it's name from the original pre-crisis Supergirl's side of the House of El living as they lived Argo City in the comics. This essentially makes her as close to Kryptonian in this series as possible. An additional homage is her family name - Kara Zor-El's mother was named Allura In-Ze, with said surname given to the show's interpretation of Kara.
This is the first cartoon to specifically state that the Green Lantern of Earth is part of the intergalactic military/police force known as the Green Lantern Corps. They patrol the farthest reaches of the DC Universe at the behest of the Guardians, a race of immortals residing on the planet Oa. For the animated Green Lantern Corps, Bruce Timm redesigned the standard Green Lantern uniform to all black with green around the collar/shoulder area, wrists, and mask.
There were some plans of having Captain Marvel/Shazam appear in an episode of this series that would also feature a fight between him and Superman, but rights issues prevented Captain Marvel and all related characters from making an appearance.
The theme song for this series is written by Shirley Walker. Producer Bruce Timm asked Walker to create a theme that instrumentally said "Superman" as he believes that's what makes a good Superman theme (i.e. John Williams theme from Superman (1978) and theme from Max Fleischer's Superman (1941) cartoons).