In an interview with The Radio Times, the Russos said Coon would be playing Proxima Midnight. She also performed some motion capture for the character as well as providing the voice. One reason for the secrecy is apparently that the Avengers 4 title alone could be a spoiler for Infinity War, so a natural place to reveal it could be with a "The Avengers will return in." title card at the end of that film.
Like most of the Black Order, Proxima Midnight was created by Hickman and Jerome Opena for the huge Thanos vs. Avengers crossover, Infinity. Proxmia Midnight is the lone female member of the group, who wields a powerful spear that can project poisonous energy. That just means more chances to see him in theaters.
He's a fearsome looking chap, and while the trailers have shown him battling against Vision, there's been no word on who might be playing him, despite an actor spotted on the Edinburgh set a year ago, who was presumably just doing the mo-cap work. That includes the film's directors, Joe and Anthony Russo, and while they're committed to avoiding spoilers for the film, they're sometimes happy to talk about what's not going to happen in the movie while still preserving as much mystery as possible. He played a character who we've called Cull Obsidian, who was in the books known as Black Dwarf. We've seen some set photos here and there, but that's about it.
That leaves Corvus Glave. He's bringing his whole Black Order with him, a group of creepy aliens who may not match Thanos in raw power, but sure do in ruthlessness.
Actors Tobey Maguire and Andrew Garfield had donned the red-and-blue suit to play the high-school superhero, but Joe - the other half of the Russo brothers - wanted someone younger for his 2016 film "Captain America: Civil War". But some speculate that Game Of Thrones actor Peter Dinklage will be the person.
Avengers: Infinity War which is the sequel to Marvel's The Avengers (2012) and Avengers: Age Of Ultron (2015), will be screened in cinemas worldwide from April 25.