The Wikipedia article for antisocial personality disorder (which is often referred to as psychopathy or sociopathy) has a quote from the Diagnostic and Statistical Manual of Mental Disorders, which is the standard criteria for classifying mental disorders. Here’s the relevant passage:
A) There is a pervasive pattern of disregard for and violation of the rights of others occurring since age 15 years, as indicated by three or more of the following:
- failure to conform to social norms with respect to lawful behaviors as indicated by repeatedly performing acts that are grounds for arrest;
- deception, as indicated by repeatedly lying, use of aliases, or conning others for personal profit or pleasure;
- impulsivity or failure to plan ahead;
- irritability and aggressiveness, as indicated by repeated physical fights or assaults;
- reckless disregard for safety of self or others;
- consistent irresponsibility, as indicated by repeated failure to sustain consistent work behavior or honor financial obligations;
- lack of remorse, as indicated by being indifferent to or rationalizing having hurt, mistreated, or stolen from another;
B) The individual is at least age 18 years.
C) There is evidence of conduct disorder with onset before age 15 years.
D) The occurrence of antisocial behavior is not exclusively during the course of schizophrenia or a manic episode.
Of those, I think Voldemort ticks quite a few boxes. Not all of them, but quite a few.
To run through them briefly: B) is trivial, C) comes from his time at the children's home, and since he's like this for his whole adult life, D) seems to follow too. There’s a little more to unpack for A), but I think we have enough to make a positive diagnosis:
- Murder, torture, the Imperius curse, etc.
Lots of examples of this one.
- The moniker “Voldemort” fits this criterion rather nicely.
- As a child, he lies to Dumbledore about his antics in the children’s home, and at school, about his work in the Chamber of Secrets. This recurs when he lies to Ginny Weasley and Harry in Book 2.
I’m mixed on this one. Sometimes,he plans very carefully. Some examples:
- Getting information about horcruxes from Slughorn, later preparing horcruxes to guard against death, and the efforts he went to in protecting them
- The events of Book 4
- Planting visions in Harry’s head before the attack at the Dept. of Mysteries
On the other hand, the series opens with him doing something impulsively:
He attacked Harry (and his parents) without being absolutely sure that Trelawney’s prophecy was actually referring to Harry. Thinking carefully, he might have realised that it could be Neville to, and taken appropriate steps.
And, of course, he attacked without the full prophecy, and would only try to find it years later when it backfired on him.
Other examples of impulsive behaviour from Voldemort/the Death Eaters:
- Entering the Ministry and allowing him to be seen by Ministry staff. If he’d held back, he might have been able to maintain the illusion that he was still dead (and the benefits that provides) for longer.
- Attacking the Quidditch World Cup
I’ll leave it up to the reader to decide if they think he meets 3 or not.
I think he’s probably quite irritable. Death Eaters and his inferiors seem to annoy him (see his dismissal of Pettigrew’s fawning, for example).
Mixed one. He certainly doesn’t care about other people; see:
- He forced Kreacher to drink the potion in the Horcrux cave, then left him to die there.
- He sends Draco to kill Dumbledore, even though he’ll probably fail, and the associated stresses as a result.
- He left Quirrell to die at Hogwarts once he’d served his purpose.
- The way he treats Pettigrew with disdain and contempt throughout the books.
On the other hand, he definitely cares about his own safety. Witness the work that went into the horcruxes; his fear of death and injury.
Hmm. Tricky one. He displays some responsibility at Hogwarts as a Prefect (else they wouldn’t have chosen him), and sounds like a conscientious and hard-working students. Then in the adult world, how does this apply to him? I can’t see Voldemort working in a corner shop. :-P
I think he probably would meet this criterion, but we don’t have enough canonical evidence to be sure.
This is weaved throughout the series, to a varying degree.
- In early life, he appears indifferent to the way he treats the other children in the orphanage.
- On “rationalizing”, he dismisses the distinction between good and evil – “There is no good and evil, there is only power and those too weak to seek it.” He cleanses the world of those he deems unworthy, and doesn’t see it as evil. (Or if he does, he doesn’t care.)
- He will casually kill devoted servants (such as Snape) if he thinks it necessary, and their service holds no weight.
IANAP, so I couldn’t give a proper diagnosis, but I think he meets enough of the criteria that it’s a reasonable claim to make.
As a bonus, note this from an interview with J.K. Rowling:
If a psychologist were ever able to get Voldemort in a room, pin him down and take his wand away, I think he would be classified as a psychopath (crowd laughs). So there are people, for whom, whatever you're going to call it – personality disorder or an illness – for whom redemption is not possible.
— An Evening with Harry, Carrie and Garp (August 2006)
I don’t know enough about psychiatry to say whether Voldemort is really a sociopath or a psychopath, and I also don’t know whether J.K. Rowling has the medical background to make an accurate assessment, but I thought it was interesting that she’d mentioned it before.