At Comic-Con 2013 last month, The Avengers: Age of Ultron director Joss Whedon revealed that Ultron is not created by Hank Pym (a.k.a. Ant-Man), giving the villain a whole new origin story that isn't from the Marvel comic books.
"It was never in my script. Because even just to sort of set up what Ant-Man does is enough for one movie. It's why I think Iron Man is extremely successful because it keeps it really simple. You have one sort of -- the villain comes from the hero's technology. It's simple. So I think why that film really works and why, sometimes, superhero films fail -- or they have mixed results -- because they have to set up a hero and a villain at the same time. And that's really tough. And sometimes it's unbalanced. You know, when I was younger I used to love Tim Burton's Batman. I was like 15 and even then I was aware, 'This is really the Joker's film.' It's like, the Joker just takes over and Batman, you really don't learn too much about him. Comics have years to explain this stuff and in a movie you have to focus on one thing. So it's about kind of streamlining, I think. Some of the most successful origin films actually have a narrower focus. You cannot put 50 years of the Marvel universe into a movie. It's impossible."