Casting Captain America is really casting two roles...Steve Rogers before and after the transformation from 98 pound weakling to perfect physical specimen. I can't divulge how we're going to do it, but the performance will be Chris Evans from beginning to end. An actor playing Captain America has to embody that backstory and let it inform his understanding of his new self. One of the interesting aspects of the character is the effect that kind of total transformation would have on the his psyche. It gives the character more dimension and the actor playing him a wider range of interesting choices.
Johnston then went on to discuss the process of how Evans came to be cast:
Chris didn't audition at all. I was already familiar with everything he'd done and was championing his cause, not that I had a fight from the Marvel team. They were fans of his as well. He came in to the art department to say hi, saw all the jaw-dropping art and designs on the wall and reacted the way I'd hoped he would. It was really his wonderful enthusiasm for everything he saw that cinched the deal. We have some of the best designers and illustrators in the industry working for us and the art is just incredible to wander through. He will bring the perfect balance of dramatic performance and physicality to the role.