Avengers: Age of Ultron
Robert Downey Jr as Iron Man and Chris Evans as Captain America in Avengers: Age of Ultron. Marvel Studios

Robert Downey Jr's Marvel contract looks set to be extended following news that the actor will reprise his role as Iron Man in Captain America 3.

The ever-reliable Variety broke the story in lieu of confirmation from Marvel, but it appears the deal is nearly set and the plans drawn up for Iron Man and Captain America to fight in an adaptation of famed Marvel comic storyline Civil War.

What does this mean for the future of Marvel's expanding cinematic universe though, and for Robert Downey Jr's continued participation in cinema's largest ongoing movie series? Let's take a look.

Robert Downey Jr

Civil War
Cap and Iron Man clash in the Civil War comic. Marvel

Robert Downey Jr was once reluctant about his future as Iron Man back when he signed a two-picture extension of his first Marvel contract, which ended with Iron Man 3. This would have taken him to an Avengers 3, but the deal looks set to change seeing as Captain America 3 will arrive before.

The actor is clearly intrigued by the planned character arc for Tony Stark: which will see him supporting a Superhero Registration Act which demands all heroes reveal their true identities to the government. Captain America (Chris Evans) vehemently opposes this act, creating the Civil War.

The reason for the act's arrival will likely be the events of next year's 'Avengers: Age of Ultron', in which Tony Stark's attempts to create a robot task force which could help heroes such as The Avengers goes awry, creating the titular maniac android Ultron.

Stark's guilt will drive his desire to support the act and will almost certainly be a key part of his story going forward.

WARNING: Potentially big (but unconfirmed) spoilers from Avengers: Age of Ultron follow...

Avengers: Age of Ultron

As mentioned the threat of Age of Ultron will be created by Tony Stark and – naturally, being a superhero movie – will nearly defeat its heroes. If rumours from several months ago are to be believed however, it could well defeat the Avengers as we know them, even if the heroes do defeat Ultron.

The rumour stated that Joss Whedon's Avengers sequel would see a rift between the group, which falls in line with a later report claiming Avengers 3 would star no Cap, Thor or Hulk, but instead Iron Man and a new group of Avengers consisting of other heroes from the Marvel universe.

This would all make sense given the rift that would be caused by an adaptation of Civil War.

Will any other Avengers appear? Marvel Studios

Captain America 3

So Iron Man and Cap will clash ideologies (and fists), but who will the other heroes side with? Marvel's Civil War comic involved almost every hero character Marvel own.

Cap 3 probably won't bring everyone together but it will at least have Scarlett Johansson and Anthony Mackie as Black Widow and The Falcon.

Falcon will certainly side with Cap, while the secretive Widow could go either way, then there's Jeremy Renner as Hawkeye, who has been rumoured for a part in the film. Could any other heroes be appearing? Iron Man will certainly need someone on his side, and Age of Ultron debutants Vision (Paul Bettany), Scarlett Witch (Elizabeth Olsen), and Quicksilver (Aaron Taylor-Johnson) are all possibilities.

War Machine (Don Cheadle) would also be likely given his involvement in Age of Ultron and closeness to Tony.

Paul Rudd will have made his debut as Ant-Man before Captain America 3 arrives as well, so throw his hat into the ring too.

Warning: Speculation about the future of Marvel's movies follows...

Marvel's Phase Three

Marvel's Phase Three of films begins with Ant-Man next summer, following Avengers: Age of Ultron. After that comes Captain America 3, which will set up the rest of Marvel's films leading up to a third Avengers film.

Doctor Strange
Cosmic mage Doctor Strange Marvel

Captain America and Iron Man coming to blows will be huge, and would open the doors for new heroes to step up.

Doctor Strange will be one of those heroes making their debut and Guardians of the Galaxy 2 is another planned film for Phase Three – though that film will likely stand separate to the Earth-bound story.

Black Panther and Ms Marvel are favourites to also get their own films in Phase Three.

The Payoff

It only makes dramatic sense for the heroes of the story to be torn apart if they eventually come back together, and that larger aim Marvel must have will surely tie to the on-going story of Thanos (Josh Brolin) and the Infinity Stones which Brolin's character is hunting down for nefarious and universe-threatening means.

With our very existence at stake, what better reason for Captain America and Iron Man to patch things up? It's a very long way off, but suddenly Marvel's grand plan seems to be coming into focus. That said, everyone assumed Thanos would be the villain in Avengers 2, and then Avengers 3, so only Marvel really know.

It sure is fun to speculate though.