Avengers: Age of Ultron

I made it through both Guardians of the Galaxy and was amused. I wonder which A-list actor is going to be in “Ultron?” After all, Robert Redford had a major role in “Winter Soldier,” and in GotG 2 Kurt Russell had a giant part as principal antagonist. Then there was Sly Stallone turning up once or twice, too. Who’s it gonna be?