The birth of the Marvel Cinematic Universe occurred in the 2008 film Iron Man, where Robert Downey Jr's take on the title character (and his alter ego, Tony Stark) was extremely important to the project's success. However, according to a new book, there was a possibility that Iron Man might not have even been Downey Jr.'s first Marvel film.
Downey Jr. was reportedly considered for a whole other armored Marvel character. The actor may have played the villainous Doctor Doom, in 2005's Fantastic Four, which was produced by 20th Century Fox, a few years before Marvel Studios even existed.
The book, The Story of Marvel Studios: The Making of the Marvel Cinematic Universe, chronicles how the massive blockbuster world came to fruition. Commenting on the birth of the MCU, Iron Man director Jon Favreau noted, “Marvel had already met with [Robert Downey Jr.] before, I think, to play Doctor Doom.”
In 2005 Downey Jr. was just hitting the tipping point in his comeback after a long history of drug problems. The actor's reputation sank after a series of arrests in 2000 and 2001, the latter leading to him getting fired from his role on the TV series Ally McBeal. He later recalled to Oprah Winfrey, "When someone says, 'I really wonder if maybe I should go to rehab?' Well, uh, you're a wreck, you just lost your job, and your wife left you. Uh, you might want to give it a shot. I said, 'You know what? I don't think I can continue doing this.' And I reached out for help, and I ran with it. You can reach out for help in kind of a half-assed way and you'll get it and you won't take advantage of it. It's not that difficult to overcome these seemingly ghastly problems ... what's hard is to decide to do it."
However, even after rehab, it was difficult for him to find work. It took Downey Jr.'s friend Mel Gibson paying his insurance bond for the 2003 film The Singing Detective to really kickstart his career once again. Producer Joel Silver then cast Gibson in the 2003 film Gothika, where Silver withheld 40% of Downey Jr.'s salary until the film was completed, as insurance against him possibly derailing the production. Downey Jr. started dating Silver's assistant, Susan Levin, during production and the two eventually married.
Despite Downey Jr.'s successful return to Hollywood, the role ultimately went to Julian McMahon, who played the part in both Fantastic Four and its 2007 sequel, Fantastic Four: Rise of the Silver Surfer.
Amusingly, Chris Evans, who played the Human Torch in both Fantastic Four movies, was then cast as Captain America in the MCU. Given that turn of events, it is possible that Downey Jr. would have still been Tony Stark even if he had played Doctor Doom.
Source: The Story of Marvel Studios: The Making of the Marvel Cinematic Universe, via The Direct