Marvel fans have been campaigning for years to have John Krasinski and Emily Blunt play Reed Richards/Mister Fantastic and Susan Storm/Invisible Woman, as they are married in real life and already have solid power couple chemistry onscreen. Krasinski has reportedly wanted to play Mister Fantastic after seeing a fan-art of he and his wife as the characters, but in an interview with Blunt, she claimed that Marvel Studios have not contacted either of them about Fantastic 4. Even if they did, she is not a fan of superhero films. Fans have also campaigned to have Zac Efron play Johnny Storm/Human Torch. Krasinski did get to play Mister Fantastic briefly in Doctor Strange in the Multiverse of Madness.
Marvel Studios regained the film rights to Fantastic Four after Disney bought most of 21st Century Fox's film and TV assets, including franchises.
Fans wanted director Brad Bird to direct the film because of his Incredibles superhero films, which were focused on a superhero family based on the Fantastic Four.
Matthew Vaughn expressed interest in directing a Fantastic Four film set in the 60s himself, similar to his work on the X-Men prequel X-Men: First Class (2011).
On the same day of the film's release day announcement, Kevin Feige confirmed that the film would not be an origin story, a decision compared to that of Spider-Man: Homecoming (2017).