Re: Characters you'd like to see in future Avengers movies?
If you want to introduce Ultron, the continuity already contains one "genius" who's inventions routinely fail in spectacularly dangerous ways: Justin Hammer. You got to figure if that guy ever tried to replicate Jarvis, he's pretty much guaranteed to end up with Ultron. I'd love to see Rockwell in a sequel. Supposedly, he's not in Iron Man 3.
"I just need to upgrade the AI a little so I don't have to... Oops."