Dr. Manhattan is one of Watchmen's most elaborate visual effects. A humanoid form in blue light, he has the power to expand and multiply. It's still actor Billy Crudup in there though, and that's definitely his voice.
Billy Crudup Talks Watchmen
"The good part was it's totally my performance so it is me moving that puppet," Crudup said. "The problem is though that the body is so vastly different that a body like that would resonate different than a body like mine. So the placement of the voice was a little bit harder to find and I think when we first saw it, or when I first saw parts of it during ADR where you're kind of looping over stuff, I was like, 'We need to tweak it a little bit and maybe change the placement of it a little bit.' Some of it was trial and error."
What they ultimately came to will hopefully sound distinct from Crudup's famous Mastercard voiceovers. "In terms of the sort of philosophy behind the voice, Zack [Snyder] had some really great ideas about how someone with that kind of ability would try to calm the people around him with not too intimidating a voice so we tried to find a placement that was not too Greek god-like. So part of it was that and part of it was just the nature of somebody who is distracted. He was not too interested in the conversations that were happening around him. He was interested in watching particles interact. So it was a strange thing to try and find. It was never totally solved but always kind of a process."
Filming the motion capture scenes, it might have been hard to maintain Dr. Manhattan's gravitas. Crudup kept a good sense of humor, especially for outrageous scenes like Manhattan's multiple entity love scene with Lori Jupiter.
"That was the page that I went, 'Yeah, I'll do this. I'll do this movie.' Yeah, I did each of those guys."
As for Manhattan's ripped physique which the ladies love, that too was a special effect. "Take a gander, my lady. As you can see, the 6' 4", 240 pound ripped version was not me. I think that guy had like 48" shoulders. I've trimmed down since then. You can't play that role for everything."