This article is an excellent look at how a Josh Blacker, a vegan actor, put on muscle and got ripped for a role as Matt Damon’s nemesis in the movie Elysium.
Remember, he was working out hard! He had to eat a lot of calories. The exercise goes hand and hand with diet.
Also keep in mind that some actors use steroids, so don’t expect the exact same results. His were killer, and could be drug free, but he also had all day to do this.