but I'm guessing since Ultron is a robot (it is right? It's not like an Iron Man suit?)
If memory serves, he was created by someone or something but was based too much on the creator and his lust to increase power and make things serve, and he rebelled against whoever made him and now wants to blow the living shit out of all living things. Basically he's a mental robot with absurd powers (and I think he's even made of adamantium too).
Quite honestly, with his powers you could give him the voice of a teletubbie and he'd still intimidate that crap out of me.