Ian McDiarmid played one of the most evil villains of all time Emperor Palatine in 5 out the 6 Star Wars movies, in the first two he played Chancellor Palpatine, and he played that character perfectly. The character was vile and manipulative and he nailed it so well it sent chills down my spine.
He also played Dr. Thomas Lancaster in the movie Sleepy Hollow, and again showed superb acting.
He is a great actor and the perfect choice to play a villain.