io9 speculates on Star trek 2 casting:
As for the other big rumored addition to the cast, Benicio del Toro is reportedly still in serious talks for the role, and it seems likely that he will be end up being cast, but his deal is still pending. He's thought to be in line for a villainous character that will be familiar to Trek fans, which many are interpreting as meaning either Khan or a Klingon of some sort, and the majority of recent reports suggest Klingons will be involved. Since sources seem to be saying it's the character, not the character's race, that will be familiar, this might mean we'll see del Toro playing a particular Klingon, the leading candidates for which would probably be the "Blood Oath" trio: Kang, Kor, and Koloth.
A familiar Klingon character of the Kirk era?
Colonel Worf, obviously.