As Ramsay...
Game of Thrones has, and has had it's share of unpleasant characters, but Ramsay may be one of the creepiest villains I've seen in years.
The psychotic nature of Joffrey, along with fighting skills and a reasonable amount of intelligence. Yuck! And he looks like a bloody maniac too.
Marvelous job by Iwan as an actor though, and from what interviews I've seen he seems like a cool person.