I just watched the trailer of Dawnguard for the umpteenth time, and noticed that the voice for the Vampire lord/king was very similar to the voice of the Daedric Prince of Domination Molag Bal. For conformation, I found a video on You tube for the quest "The House of Horrors" and just compared the two voices.

(For some reason I can't paste the URL for the videos. So, I recommend just searching yourself)

I totally hate your tags.

Anyways, no, it is not Molag Bal. He could, however, worship Molag Bal since the emblem on his armor and the fountain of blood is the same symbol as Molag Bal's mace. And Molag created vampires.

Umm no...not Molag Bal...

No, because the guy in the trailer does not say "soooouuullllaahh!"

I never had any reason to think the voices would be remotely similar.

No, I believe they're just voiced by the same person.