Editing Superman (2025) (section)

=== Pre-production ===
Production design, costume design, and the casting process began in April 2023. [[Beth Mickle]] and [[Judianna Makovsky]] returned in their respective roles as production designer and costume designer from ''The Suicide Squad'' and Gunn's ''[[Guardians of the Galaxy Vol. 3]]'' (2023). Filming was set to begin in January 2024. Gunn was looking for an actor to play Superman who possessed the character's humanity, kindness, and compassion, and was "somebody who you want to give a hug". He said the character Jimmy Olsen would appear, and that he was not looking to make the film a comedy. He hoped ''Legacy'' would be different from previous ''Superman'' films while still respecting what came before. Gunn turned in the first draft of the script at the end of April and the production was not expected to be impacted by the 2023 Writers Guild of America strike when it began in early May.

Audition tapes for the main roles of Superman, Lois Lane, and Lex Luthor were submitted by early May. Gunn began watching them later that month, while he was storyboarding the film. [[David Corenswet]] was a top contender for Superman and was set to do a screen test at the end of the month or in early June. Other actors in consideration included [[Jacob Elordi]], [[Tom Brittney]] and [[Andrew Richardson]]. Elordi declined to read for the role, feeling that it would be too dark for him. [[Emma Mackey]], [[Rachel Brosnahan]], [[Samara Weaving]] and [[Phoebe Dynevor]] had tested for Lane; Dynevor was one of the final contenders for that role. [[Nicholas Hoult]], the runner-up to play [[Batman (character)|Batman]] in ''[[The Batman]]'' (2022), was eyed for Luthor but chose to pursue the role of Superman. Gunn was considering A-list actors with whom he had previously worked for Luthor, and discussed the role with a ''Guardians of the Galaxy Vol. 3'' actor that was reported to be [[Bradley Cooper]]. Black actors were also being considered. Testing took place using the label "Apex", a reference to a comic version of Luthor called Apex Luthor. Other comic book superheroes were expected to already be established in the film's setting, with casting underway for a Black actor to play Michael Holt / Mister Terrific and for an Asian or Latinx actress to portray a character labeled "Blitz". [[Pierson Fodé]], who appeared in an episode of Supergirl (2015–2021), submitted a self-tape for Superman by the start of June which Gunn reportedly liked.

In-person screen tests took place at the Warner Bros. lot in Burbank, California, with Gunn and Safran in mid-June. The actors tested in makeup and costume as Kent and Lane in the following pairs: Hoult and Brosnahan, Brittney and Dynevor, and Corenswet and Mackey. The Kent contenders then tested in costume as Superman against Mackey. Gunn edited the tests together to be played for a deciding committee that included Zaslav, and the casting of Corenswet as Superman and Brosnahan as Lane was announced on June 27. Casting for other roles was set to follow, including for members of the superhero team the Authority, who were expected to be introduced in ''Superman: Legacy'' ahead of their own film. Brothers [[Alexander Skarsgård|Alexander]] and [[Bill Skarsgård]] were on the shortlist for Luthor. It was unclear if Hoult would return to try for Luthor again. On July 11, two years before the film's scheduled release date, the casting of [[Isabela Merced]], [[Edi Gathegi]] and [[Nathan Fillion]] as the respective superheroes Hawkgirl, Mister Terrific and Guy Gardner / Green Lantern was announced. [[Anthony Carrigan]], who had expressed interest in playing Luthor, was cast as the superhero Rex Mason / Metamorpho the next day. Gunn had chosen some of these actors some time earlier, but had been waiting until Superman and Lane were cast before negotiating further actor deals, leaving little time to complete negotiations before the 2023 SAG-AFTRA strike began on July 14. In response to concerns that the other superheroes would take away from the story of Superman and Lane, Gunn said those two characters remained the focus of the film and the other actors were being cast for multiple DCU projects.

When the WGA strike ended in September 2023, ''Superman: Legacy'' was expected to begin filming in early-to-mid 2024. [[Jason Momoa]], who portrayed [[Aquaman (character)|Aquaman]] in the DCEU, was reported the following month to have discussed portraying the character Lobo in either ''Superman: Legacy'' or a solo film. The SAG-AFTRA strike ended on November 9, and filming was clarified to be beginning in March 2024. Gunn said the film would still make its July 2025 release date. [[María Gabriela de Faría]] was revealed to be cast as Angela Spica / The Engineer, one of the film's antagonists and a member of the Authority, in mid-November. Singer [[Madison Beer]] said she submitted a self-tape and unsuccessfully auditioned for an undisclosed role, as did [[O'Shea Jackson Jr.]] Hoult was in talks to portray Luthor prior to the SAG-AFTRA strike, and negotiations for the role were continuing in November, when [[Sara Sampaio]] and [[Skyler Gisondo]] were revealed to have been respectively cast as Luthor's assistant Eve Teschmacher and Jimmy Olsen. Gunn said Gisondo, Sampaio, and de Faría had been cast prior to the strike, and the roles of Mister Terrific and Teschmacher were particularly difficult to cast and required many auditions. Journalist Jeff Sneider noted speculation that the character Sam Lane would appear and indicated that [[Michael Rooker]] was linked to the role, but Gunn denied that Rooker would play the character.

In December 2023, Gunn's brother [[Sean Gunn]] was cast as Maxwell Lord for future DCU projects, after [[Pedro Pascal]] played the role in the DCEU film ''[[Wonder Woman 1984]]'' (2020). The character was expected to be referenced in ''Superman: Legacy'' but it was unknown if he would appear in the film. James Gunn confirmed that Hoult had finalized a deal to portray Luthor, and [[Miriam Shor]] entered negotiations for an undisclosed role after appearing in ''Guardians of the Galaxy Vol. 3''. The Hollywood Reporter also said the cast included Sean Gunn and [[Pom Klementieff]], who starred in the ''Guardians of the Galaxy'' films, before James Gunn stated that Klementiff was not involved in the film and Shor had not been cast. He added that the film's script had been mostly completed prior to the writers' strike. Gunn said in January 2024 that work on the sets, prosthetics, and visual effects models were underway, the costumes were being completed, and most of the actors had been cast, while Brosnahan said the film was being made with a lot of love for the source material, as many cast and crew members had grown up watching Superman films and reading the comics. At the end of the month, [[Milly Alcock]] was cast as Superman's cousin [[Supergirl (character)|Kara Zor-El / Supergirl]]. The character was reported to be making her debut in ''Superman: Legacy'' ahead of starring in her own DCU film, ''Supergirl: Woman of Tomorrow''. Alcock had performed auditions and screen tests in costume on the ''Superman: Legacy'' set in Atlanta, Georgia, earlier in January.

Pre-production work in Ohio began in early February 2024. Later that month, [[Bassem Youssef]] said he had been cast in the film — reportedly as Rumaan Harjadi, the leader of a fictional Middle Eastern country — but his character had been removed from the script. He believed this was potentially due to comments he made in October 2023 criticizing the Israeli government during the Israel–Hamas war, although this was soon disputed by reporters. Gunn confirmed their reports, saying he discussed a role with Youssef, who had not been formally offered the part, prior to the WGA strike, but the character was removed from the final script after the strike ended and before Youssef's comments. At that time, the Ohio Department of Development announced that ''Superman: Legacy'' was set to film in Cleveland and Cincinnati, Ohio, and was awarded over $11 million to film in the state through its tax credit program. Gunn held a table read with the cast on February 22, and revealed that [[Terrence Rosemore]] was portraying Luthor's henchman Otis after having small roles in some of Gunn's prior films. Zaslav confirmed that filming was set to begin the following week.