It takes a lot of people to make a movie happen. It takes producers and directors and an entire cast and crew. However, sometimes they still require a little help from people who aren't even directly involved in the production. Such was apparently the case when it came to Academy Award nominee Zero Dark Thirty. Jessica Chastain was offered the lead in the film by director Kathryn Bigelow and Chastain really wanted to make the film. Unfortunately, she was already under contract to star alongside Tom Cruise in the science fiction film Oblivion. As it turns out, this wasn't the issue that it could have been, as Tom Cruise was willing to let Chastain out of the contract in order for her to make Zero Dark Thirty.
Jessica Chastain was originally cast in the role of Julia, which eventually was played by Olga Kurylenko when Oblivion finally made it to the screen. Chastain would go on to star as a CIA agent who has been working to track down Osama Bin Laden following the September 11 terrorist attacks. Chastain would be nominated for an Academy Award for Best Actress for the role. Oblivion would go on to make nearly $300 million at the box office.
Scheduling conflicts are the single most used explanation for why a particular actor or director did not take on a particular film. While sometimes there's some question as to exactly how legit that explanation is, in this case, it certainly seems to have been the case. Jessica Chastain told The Hollywood Reporter that she really did want to make Oblivion as well, but that she just wanted to make Zero Dark Thirty that much more. Don't be surprised to see Tom Crusie and Jessica Chastain in a movie together at some point down the road. Chastain says she's still very interested in working with the Mission: Impossible actor, calling him "awesome" for being willing to let her out of her contract.
Movie making is a business and as such, sometimes decisions have to be made for business reasons. Movies have to be produced and released within certain timeframes because there's a studio that is expecting to see revenue coming in at certain times. This means that most of the time movies have to go with the actors that are available at the right time. It's not uncommon for a movie's schedule to be built around its lead actor, but the supporting cast rarely if ever has that luxury.
We'll always wonder how movies might have turned out with other actors in iconic roles, yet we can't really imagine anybody else but Jessica Chastain in Zero Dark Thirty. We can apparently all thank Tom Cruise for the opportunity.