YES. Scott Tenorman’s parents.
And then he taunted Scott with “I made you eat your parents, I made you eat your parents.”
He later found out Scott was actually his half brother.
As in Bocce?
This far in and nobody’s mentioned Snidely Whiplash?!? 
I agree. Master of science and sorcery. Darth Vader is a pale knock off.
And like Mr. Bester above, she brings the most out of the characters she interacts with:
Devotion from Spike, Macho Bullshit from Angel, whatever the hell it is between her and Darla…
Juliet sold both sane and crazy very very well.
Has anybody cited Webcomics?
Drip Rat from the webcomic JACK.
A rapist and serial killer who, upon death, became an arch-demon…the very embodiment of the Deadly Sin LUST…and the main enemy of the titular Jack, himself the Sin of Wrath and tasked with the duties of the Grim Reaper, shepherding the newly dead to judgement.
Tarquin
Xykon
Red Cloak
The Linear Guild was boring. I was glad when Malack…
What is a Bocce?
A juvenile dick.
Looking back through this tread I’m shocked that Vincenzo Coccotti from True Romance was overlooked.
Traditionally, Eric Von Stroheim was billed as “The Man You Love to Hate,” but the parts that stood the test of time: Sunset Boulevard and Grand Illusion, are sympathetic characters.
J. T. Walsh played a prick better than any other actor of his generation. Everyone has had someone like his characters inflicted upon them at some point in their lives.
Cyril Cusak, of Fahrenheit 451, 1984, and Day of the Jackal, excelled at the banality of evil, his characters have so completely accepted their own sadism and corruption that they’ve grown bored of it. And, as a product of the Irish theatre, Cusak had a more natural acting style than the Shakespearian Brits who generally get all the attention for villainy, including his son-in-law Jeremy Irons.
Roy Batty of Blade Runner. Eminently quotable and not just for his tears-in-rain speech.
I’ll second Victor von Doom. He always seemed a classy villain, and his armored costume had style. I’m convinced that George Lucas stole the image to create Darth Vader, just adding a Samurai Kabuto helmet with a futuristic-styled faceplate. He already had the armor and the hooded cape.
Not only that, Doom was portrayed as offering his enemies dinner more than once:
Again, I suspect these gave Lucas the idea for the Dinner with Darth Vader scene in the Cloud City in *The Empire Strikes Back.
For me, inhuman villains–be it the Borg, the Goblin King, or Dracula–are less scary than human villains. Especially villains that are governed by instinct or magical code or programming code can be cool, but they’re more like forces of nature than personally repugnant villains.
So I’ll propose one I haven’t seen so far: Killgrave, from Jessica Jones. A child who was tormented and experimented on by terrible parents, he develops mind-control powers, and he uses them to rape and murder and enslave people around him with zero regard for their humanity. The casual violence he inflicts on those around him made my skin crawl in the best possible way.
IIRC, “My evil parents did medical experiments on me, and that’s why I’m this way,” was Killgrave’s self-serving spin on his childhood. While he did undergo experimental medical treatments, they were because he was born with a degenerative neurological disease, and they were trying to find a cure.
As an aside, we learn in the TV show that Killgrave isn’t his real name, and his parents named him Kevin. I always wondered if that was a reference to the film, We Need to Talk about Kevin, about a mother dealing raising a kid whose a violent sociopath.
In what way is he even a villain?
Reading the wiki, it sounds like you’re right. The experiments weren’t frivolous; they were life-saving. Nevertheless, they were torment, and his parents didn’t exactly win any Parents of the Year awards for how they connected with him during that process.
Which isn’t to excuse him, obv; but it makes a character interesting if their motives for being awful have some underlying logic.
Baron Harkonnen from Dune.
And all his creepy relatives, too.
Was it necessary to kill J.F. Sebastian or Hannibal Chew?
My recollection is his parents were normal parents dealing with a very ill child, and Kilgrave’s complaints were just narcissism and self-justification, but I could be misremembering, or maybe it was deliberately ambiguous about where the truth was between their two versions. I do kind of prefer the “He had a loving and supportive family until he made his mother hold a hot iron to her face,” version, just because of how absolutely and completely evil it makes him.
Plus, “Victims of abusers become abusers themselves,” is a tired and problematic trope, particularly in the context of a story about an abuse survivor. Making him evil ex nihilo makes for a stronger story.