However, the casting call also includes massive spoilers about the plot, that confirm what writer-director Joss Whedon revealed about the villain Ultron getting a new origin. Be warned, there will be spoilers contained below, so read on at your own risk.
"In The Avengers: Age of Ultron Loki is gone and the new villain will be the evil robot Ultron, who has the ability to keep upgrading his own strength, making him extremely fearsome. Tony Stark/Iron Man becomes the unwitting creator of Ultron. The brother-and-sister team of Quicksilver and the Scarlet Witch become the seventh and eighth members of The Avengers. Quicksilver has extreme speed, while Scarlet Witch can cast spells and has telekinesis ability. Black Widow and Hawkeye will be key figures in the film."
In the Marvel comic books, Ultron was the creation of Hank Pym, a.k.a. Ant-Man, a character who is getting his own movie directed by Edgar Wright that will kick off Marvel Phase Three on November 1, 2015.
Avengers: Age of Ultron comes to theaters May 1st, 2015 and stars Aaron Taylor-Johnson, Scarlett Johansson, Robert Downey Jr., Elizabeth Olsen, Chris Hemsworth, Chris Evans, Cobie Smulders, Jeremy Renner. The film is directed by Joss Whedon.