I'm thinking of all the grasping, selfish schemer's who have no regard for others in the Black Adder universe...Evil but not Serial Killer Rapist Evil.
You don't have to be a sociopath to be Evil, you can just be selfish enough to make the grade.
Re: Cartoon Evil, I guess I exaggerated the "comical" view of evil, to show it can be fun/humorous instead of dark/twisted. But I am thinking of "real life" evil aligned examples that aren't psychopaths. Schemers, thugs, black marketeers, art thieves, corporate spies, etc. People that do extremely unethical things to better themselves.
You keep coming back to psychopathic serial killers. But really, c'mon. They aren't the only Evil characters folks play. What you're dismissing as psychopath the CE "Do what I feel like with no control and no goal". The best example of this would be the Joker from Batman: The Dark Knight; the Joker wants to burn it all to the ground, because the world needs to burn.
What you describe in your campaign IS a sociopath. A sociopath is just someone who cannot empathize with others because they can't feel emotions. They see other people as not being "real", only tools to be used. Sociopaths excel at manipulating others by mimicing the behavior of emotions. You just typically don't hear about the successful ones because they're... successful. They found a job where having no ability to empathize is useful.
And c'mon. Art thieves don't have to be evil.
I would use any sort of mastermind in any sort of tense thriller movie. Swordfish, Taking of Pentlam 123, several I would use any sort of mastermind in any sort of tense thriller movie. Swordfish, Taking of Pentlam 123, several Die Hard movies, etc. Generally the villain is both methodical AND heartless.
When it comes to Evil PCs, I would actually look at villains. Typically, your villains in books/movies are not villains in their own right. They are not heartless bastards. A good villain, in general, does not consider themselves evil. They consider themselves utterly justified in doing what they do, and view themselves as heroes of their own story. Dr Freeze is trying to save his wife, for instance. Vader is corrupted, and eventually has lost everything, leaving him do what he has made himself. Lucifer rebelled because he loved God too much to bow down to Man.
So an Evil PC isn't a cackling crazy person. If, for instance, Necromancy in your world is evil, then the Pc could just be a necromancer. Not because he wants to create an army of zombies and rule the world with a rotting fist, but he just wants to
practice necromancy. Maybe he wants mastery over death in order to STOP death from ever occuring. Maybe he wants immortality for himself.
Having a
reason for that evilness beyond "Yeehaw we're evil!" produces depth. Look at the PC as if they were a villain in someone else's story, and ask, "How interesting is this?"