Sociopath- a person with a personality disorder manifesting itself in extreme antisocial attitudes and behavior and a lack of conscience.
http://www.ranker.com/list/the-best-sociopaths-_functional_-in-film/stokified,
Darth Vader
Star Wars
Travis Bickle
Taxi Driver
Joker
The Dark Knight
Bane
The Dark Knight Rises
Loki
Thor
John Doe
Se7en
Sgt. First Class William James
The Hurt Locker
Kahn
Star Trek: Into Darkness
The Emperor
Star Wars
Gaear Grimsrud
Fargo