Nocturian

I'm not sure I've heard of the storm lord though typhus is quite powerful so perhaps him

I did some comparing between their tabletop versions and it seem Typhus is a bit more powerful, though they are not that far removed, Imothek is one of the strongest necron overlords out there after all

http://imgur.com/ZNjo42H

I suspected he was a necron but typhus is a first captain of a chaos space marine legion who is also the herald of nurgle himself and a psycher to boot