So this could be inaccurate information, but would be a bit odd if it was. I say that because we know Joss Whedon is still working on the script for Avengers: Age of Ultron (aka The Avengers 2), but since this is more a simple plot description, it could be legit. So according to a casting call listing, we might just know who is responsible for the creation of Ultron now. Whedon has already said it won’t be Hank Pym, the “father” of Ultron in Marvel Comics. Which I still don’t understand why it can’t be Hank Pym, not like he has to become Ant Man (or Giant Man) within the same film. Any ways, the description reveals the following (SPOILER!):
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. (Hi-Lite to read →)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.