One of the biggest things many fans were surprised about was the facet that Ultron's creator in Avengers: Age of Ultron would not be Hank Pym but be Tony Stark, Hank Pym originally created the villain the comics.
In a previously unpublished portion of an interview with Empire Magazine in April 2014, director Joss Whedon explains why that decision was made.
“Of all the heat I’ve ever taken, not having Hank Pym was one of the bigger things,” Joss Whedon told Empire.
“But the fact of the matter was, Edgar [Wright] had him first and by virtue of what Edgar was doing, there was no way for me to use him in this. I also thought it was a bridge too far. Ultron needs to be the brainchild of the Avengers, and in the world of the Avengers and the MCU, Tony Stark is that guy. Banner has elements of that guy – we don’t really think of him as being as irresponsible as Tony Stark, but the motherf***er tested gamma radiation on himself, with really terrible, way-worse-than-Tony-Stark results.”
He also explained that Ant-Man being the next movie released after Avengers: Age of Ultron, was there not a place for Hank Pym?
“It didn’t make sense to introduce a third scientist, a third sciencetician,” Whedon explains. “It was hard for me, because I grew up on the comics, to dump that, but at the end of the day, it’s a more interesting relationship between Tony and Ultron if Tony was once like, ‘you know what would be a really great idea?’ They’re doing what they always do – which is jump in headfirst, and then go, ‘Sorry, world!’ But you have to make it their responsibility without just making it their fault.”
Avengers: Age of Ultron is set to open in theaters May 1 this year.