A Black Ops Question?

I've been playing Black Ops for awhile and the question struck me. In zombies: How does Mason have anything to do with it. Like he's sitting at the chair and there's the Zombie selection part but why isn't he involved in any of them? Theres Dempsey, Nikolai (BTW is my fav), Takeo, Richtoffen, JFK, Nixon, Cuban Dictator (I KEEP FORGETTING HIS NAME!!!!) McMarmion, and the new characters for Call Of The Dead. But no Mason. Is it becasue of Nova 6? Like he knows what it is and what it done to people so he knows of Zombies or something?