Originally Posted by Chewy
The reason Ultron works as a villain is that his existence takes a relatively good man and ultimately destroys every meaningful aspect of his life. Pym is the ultimate tragic hero.
No way would Marvel be willing to deconstruct Stark like that, nor should they. And without that aspect of the story Ultron is just another killer robot.
I'd go with making Ultron some piece of rogue Stark tech, myself. Aside from not knowing whether the movie Ant-Man is going to be Eric O'Grady, Hank Pym, or Scott Lang, an artificially intelligent robot seems more like something Stark would build rather than someone like Pym, who's a biochemist. Just because Stan Lee didn't care/realize how specialized the sciences were forty years ago doesn't mean the movies shouldn't try to do better.