Robert Downey Jr. Joins 'Captain America 3' For Civil War Storyline

Well, now we know what all of Robert Downey Jr.'s vague promises of "plans" and "other stuff" with Marvel were about. The actor is reportedly in final negotiations to join Chris Evans' titular hero in Captain America 3.

Even more exciting is what he'll be doing there: Going head to head with Cap in an adaptation of the Civil War storyline from the comic books. Hit the jump for all the details on the Robert Downey Jr Captain America 3 casting.

Eventually, Rogers and other superheroes are forced to go on the run to avoid arrest. Effectively, this makes Tony Stark the villain of Captain America 3. The meaty premise also gives the Marvel Cinematic Universe plenty to work with over the next several films leading up to Avengers 3 and 4, as various characters find themselves dealing with the fallout or grappling with the thorny issues raised by the Superhero Registration Act.

What slightly off about Civil War as Phase 3 in the MCU is that in the comic books, the question of secret identities is a big sticking point. There are no secret identities in the movies, so the Civil War storyline will have to be altered. Marvel's done this before. Age of Ultron was modified from the comic to screen and Tony Stark's trouble with booze was alluded to but never directly addressed.

(Also worth noting is that Spider-Man plays a major role in the original Civil War. And Marvel is relaunching the storyline in the comic books in 2015  with this photo of Spider-Man being torn between Captain America and Iron Man.)

Presumably the events and destruction of Avengers: Age of Ultron, whatever they may be, will kick off the battle between Stark and Rogers. After Ultron, Marvel introduces a new character in Ant-Man and then Captain America 3 comes along, continuing the Age of Ultron storyline much in the same way Captain America: The Winter Soldier continued The Avengers.

The Civil War news also leaves us wondering how the plot arc will fit with the Infinity Gauntlet/Thanos storyline that has been ramping up over Phase 1 and Phase 2. Is that now slated for Phase 4? Is that the big event that finally gets all the superheroes back together? We'll have to wait and see about all that.

Back to reality, one interesting note in the trade is Downey almost didn't appear at all. Marvel originally wanted him for a smaller role, but Downey lobbied for more screen time (and therefore more money). Marvel Entertainment chief Ike Perlmutter was so angry he ordered screenwriters to cut Downey out of Captain America 3 entirely. But the two sides kept talking, and eventually they came to a deal.

Ultimately, Downey is expected to collect about $40 million plus backend on the deal plus another bonus if Captain America 3 does better than Captain America: The Winter Soldier. Which it probably will, because Iron Man is still arguably the Marvel Cinematic Universe's best known hero. The new film is not covered by his current contract, which only takes him through Avengers 3.

Captain America: The Winter Soldier directors Joe and Anthony Russo are back to helm Captain America 3, and are currently working on the script with Christopher Markus and Stephen McFeely. Captain America 3 shoots next spring for release on May 6, 2016. Expect an official announcement, along with a title, very soon.