People here and on the Web generally have established that Sherlock is not a sociopath and that Moriarty most likely is a psychopath. Can we say that Magnussen from Sherlock season 3 has any disorders of that kind? If we can, what'd be the grounds?
Magnussen is by far the least desirable characters, from the entire Sherlock series. I don't think he suffers from any disorder but he is definitely a megalomaniac. He loves to hog the limelight and is a complete totalitarian. Example, peeing in the fireplace:
MAGNUSSEN: ... you’re so domesticated. All standing around, apologizing ... (He nods to Sherlock and then walks in between him and John towards the fireplace.)
MAGNUSSEN: ... keeping your little heads down. (He stands in front of the fireplace, facing it. The sound of him unzipping his trousers can be heard.)
MAGNUSSEN: You can do what you like here. No-one’s ever going to stop you. (He looks down and the sound of him urinating into the fireplace can be heard. John blinks as if appalled and half-turns his head towards him. Sherlock keeps his head facing forward, his eyes fixed on the opposite wall.)
MAGNUSSEN: I’ve interests all over the world but, er, everything starts in England.(He looks down again as the last of his urine splashes on the grate in front of the fire.)
MAGNUSSEN: If it works here ... (He jiggles up and down as he ‘shakes off’ and then zips up his trousers.)
Though Sherlock acknowledges himself as a high functioning sociopath, Magnussen on the contrary acknowledges himself as a businessman. This is evident from the scene where armed police marksmen run towards Sherlock, John and Magnussen outside the appledore.
JOHN (looking round to his friend): Sherlock, what do we do? (He turns to look at the helicopter again.)
MAGNUSSEN (over his shoulder): Nothing! (He looks round at them.) There’s nothing to be done! Oh, I’m not a villain. I have no evil plan. I’m a businessman, acquiring assets. You happen to be one of them!
On the whole, I thing Magnussen is just a malicious mogul who uses the mind mapping technique.
Source for transcript: Arianedevere