Originally Posted by JB-the-Hunter
Maybe that means each of the Avengers will have a hand in creating Ultron. Tony builds him, Banner does some of the brain wave type stuff. Steve teaches him how to fight or something like that. Maybe Ultron is essentially the Avengers combined.
I suspect this is whats happening. its going to be one of theose scenarios in which every Phase II movie will have something that links to Ultrons creation, but it will be vague enough that we won't notice it. And then Avengers 2 comes along and explains it all and we'll be like "oh we should have seen that coming"
In IM3 for example i'm betting that 'empty brain slot' thing that Killian talked about is going to show up again and play a part in this.