There's a new rumor going around that he also might be Garth of Izar or whatever.
From what little knowledge of the Star Trek Universe that I have, I'm going to go with Kahn because the line in the trailer is, "For I have returned to have my vengeance!" That sounds a lot like Kahn to me.
Also....the Japanese trailer gives us just a couple seconds of additional footage that points more toward Kahn than it does Gary Mitchell: LINK
Fast forward close to the end to see what I'm talking about.
This post was edited on 12/6 at 9:09 am