After Iron Man helped put comic book adaptations back into the plans of every film studio in Hollywood in 2008 (by proving that "B-List" superheroes can launch franchises if done right), Marvel Studios rushed to develop what became known as Phase 1 of the Marvel Cinematic Universe. Iron Man 2, Captain America and Thor were all quickly greenlit alongside The Avengers, the film that would bring all of theses characters together.
For Thor, Marvel enlisted William Shakespeare aficionado Kenneth Branagh to direct the first big screen foray into the Marvel's version of the nine realms of Norse Mythology and the golden metropolis known as Asgard. Like Captain America: The First Avenger, the film was a success and earned a followup, and also like Captain America, its followup was helmed by somebody else. Anthony and Joe Russo took over from The First Avenger director Joe Johnson to helm Captain America: The Winter Soldier (and are back for Captain America: Civil War and the next two Avengers movies) and Thor: The Dark World served as the feature film directorial debut for Alan Taylor (Game of Thrones).
Taylor wasn't as great a fit with Marvel as the Russos were though, and just like it was clear early on that writer and director Joss Whedon would part ways with Marvel after Avengers: Age of Ultron, when we met Alan Taylor on the set of The Dark World, the constantly-in-flux process of making a massive Marvel production on a tight schedule didn't sit well. We knew he wouldn't help Thor 3. And he's not. It might actually be Kenneth Branagh who returns, if the latest rumors are to be believed.
The subtitle of the third Thor movie was revealed in October at Marvel's fan and press day where they unveiled the release schedule and titles for Phase 3 of the Marvel Cinematic Universe. Thor: Ragnarok, which is being written by Craig Kyle and Christopher Yost, would open in theaters in 2017, and it surprised no one. Kyle, who produced The Dark World, has long hinted that the next Thor would likely touch on the Ragnarok event from the comics.
Heroic Hollywood's Umberto Gonzalez appeared on Popcorn Talk and revealed that Branagh may have been offered the director's chair for Thor: Ragnarok, that Marvel wants to work with him again. He's allegedly also being offered a chance to direct Twentieth Century Fox's take on the Agatha Christie classic Murder on the Orient Express Film, so that would be a conflict should he choose the latter.
Ragnarok, according to Marvel Studios president of production and super producer Kevin Feige, has a major part to play in the bigger story of the Marvel Cinematic Universe and its title implies Asgard is in for a reckoning. That means Marvel needs to find a director who can handle a large ensemble of characters and large-scale, fantastical action. Thor wasn't a homerun for critics, and Branagh didn't fare too well with Jack Ryan: Shadow Recruit, but he did put himself back in the good graces of Disney after the critical and financial success of Cinderella. Interestingly enough, while promoting Cinderella this spring, Branagh did say he'd be open to working with Marvel again if the right gig came along. If anything, Branagh was instrumental in the tremendous casting of Thor, characters of which still remain some of Marvel's best.
The real question however, is whether or not the mighty Thor will actually wear his helmet...
Update: Edited statement about Iron Man's opening.
Ant-Man opens in theaters July 17, 2015; Captain America: Civil War – May 6, 2016; Doctor Strange – November 4, 2016; Guardians of the Galaxy 2 – May 5, 2017; Spider-Man reboot – July 28, 2017; Thor: Ragnarok – November 3, 2017; The Avengers: Infinity War Part 1 – May 4, 2018; Black Panther – July 6, 2018; Captain Marvel – November 2, 2018; The Avengers: Infinity War Part 2 – May 3, 2019; Inhumans – July 12, 2019.
Source: Popcorn Talk (hat tip Nick)