10. Hammer Industries
Justin Hammer is arguably the man who despises Tony Stark the most, as he was everything he wanted to be and his weapons were simply superior. As a rival weapons contractor, Hammer wanted Stark's technology and, when he tried to defeat Stark and destroy his legacy, he failed miserably. Any opportunity to take Stark down would likely be exploited by Hammer and Ultron's emergence could be that opportunity. I picture Hammer approaching Ultron, much in the same way that Lex Luthor approached General Zod back in the Christopher Reeve movie days, with a plan to work in accordance with the robot for a mutually beneficial end - in this case, the taking down of Tony Stark. Ultron would get the resources of Hammer Industries to create his droids to help him take over the world and Hammer would get the satisfaction of seeing Tony Stark defeated and the promise of safety in Ultron's new world. Sam Rockwell was the best thing about Iron Man 2, so Marvel really should think about using him again and this could be the ideal opportunity.