34. The Trinity Killer, 'Dexter'
Talk about killer casting. Actor John Lithgow had long walked the line between manic and maniac in his performances, comedic or otherwise, but his role as Arthur Mitchell — the so-called "Trinity Killer" was — saw him leap that line in terrifying fashion. Initially seen as a family-man role model, he's revealed to be Dexter's most prolific and disturbing murderer — evil in a way not even our homicidal antihero can stomach. This makes him the titular killer of killers' most formidable target; it also places the people Dexter cares about in grave peril, as he learns to his lasting devastation.