When asked if Nathan Fillion's Guy Gardner would have his iconic bowl cut in the film, James Gunn replied "Giving my old pal Nate a bowl cut might have been my primary reason for casting him."
James Gunn tweeted that the death of his father was an influence on the screenplay. The film's release date, July 11, 2025, was his father's birthday.
James Gunn has assured fans that the movie is not a comedy and that, despite adding several other DC Comics characters, the story focuses on Clark Kent/Superman and Lois Lane.
The inclusion of Nathan Fillion as Guy Gardner marks the seventh time that Fillion has appeared in a film directed by James Gunn, continuing the tradition of the actor making an appearance in every one of Gunn's films, owing to the pair's longtime friendship.
Milly Alcock is set to make an appearance as Kara Zor-El/Supergirl. This could mark the very first time Superman and Supergirl appear on screen together in film. The Flash (2023) makers used CGI and artificial intelligence to bring them together, featuring Christopher Reeve and Helen Slater's likenesses.