Marvel Studios is in final talks with Robert Downey Jr. to star in Captain America 3, which will introduce the popular Marvel Civil War comic book story line to the Marvel Cinematic Universe.

The story will pit Robert Downey Jr.'s Iron Man/Tony Stark against Chris Evans' Captain America/Steve Rogers, as they feud over the Superhero Registration Act, which forces anyone with super-human abilities to register themselves with the U.S. government, and agree to serve as part of a new police force. Stark supports the program, but Rogers does not, believing that it threatens the civil liberties of U.S. citizens. Rogers and others opposing the act are forced to go on the run. This story will also enable Stark to be a villain, of sorts, with his views going against the rest of his Avengers teammates.

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Production is set to begin in the spring of 2015, with a May 6, 2016 release date already slated for the sequel. Variety reports that while a deal for Robert Downey Jr. to star in Captain America 3 is nearly finalized, it almost fell apart.

Marvel originally wanted the actor for a small role that would have only required three weeks of work on set, but Robert Downey Jr. wanted Tony Stark to be a much bigger part of the story, which naturally results in a bigger payday for the actor. Sources indicate that Marvel Entertainment chief Ike Perlmutter was so enraged that he ordered the screenwriters to write Iron Man out of the script. However, Marvel Studios president Kevin Feige continued negotiating with the actor's reps, and tried to convince Perlmutter to see his grand vision for the Marvel Cinematic Universe, and how the introduction of the Civil Wars story line would help drive new franchises and sequels for the next seven years.

The fallout from the government's and Stark's action will be a driving force in The Avengers 4, while helping to introduce new characters like Doctor Strange and even Ant-Man, which hits theaters in July 2015.

Sources claim that Robert Downey Jr. will earn $40 million from Captain America 3, plus a portion of the profits on the back end, and bonuses if Captain America 3 outperforms this year's Captain America: The Winter Soldier, which earned $714 million worldwide. The actor took home $50 million for Marvel's The Avengers in 2012.

The actor is also under contract to star in The Avengers 3, and he will next be seen in 2015's Avengers: Age of Ultron. There was a report from last month that hinted The Avengers 3 may introduce a whole new team, with actors like Robert Downey Jr., who are nearing the end of their deals, being saved for an unspecified movie. It isn't clear, at this point, if the actor's new deal is just for Captain America 3, of if he has signed on for The Avengers 4 as well, since The Avengers 3 is believed to be the last movie the actor is under contract for.

Anthony Russo and Joe Russo (Captain America: The Winter Soldier) are returning to direct Captain America 3 from a script by Christopher Markus and Stephen McFeely. The directors revealed last month that there is "a very big idea" at the center of Captain America 3, which now appears to be the Civil War story line. Captain America: The Winter Soldier star Frank Grillo is expected to return as Crossbones.

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