Originally Posted by regnak
Maybe Ultron builds the Hulkbuster as a drone. If he has access to Stark's tech/blueprints then it would be feasible and would sow distrust among the inferior humans!
I just picture us catching up with their bromance early in the film in the Avengers Tower, while they are messing around with the Hulkbuster build. Maybe Banner purposely Hulking out so Stark can do some metrics for his design. Prolly not the case though.