Hannibal Lecter

do the flying monkeys on the Wizard of Oz count?

Javier Bardem as Anton Chigurh, the hitman in No Country for Old Men.

Mojo Dojo from the Powerpuff Girls.

Yahweh, for mass genocide, ethnic cleansing, and the near obliteration of the human race, yet maintaining a loyal following. That's some true wickedness right there.

Okay, serious answer: I'm drawn to villains that are flawed but not in a cartoonish way. I like them to be people with hopes and dreams, but who have something deeply wrong with them. Perhaps their horrific acts are the result of blind anger or a mental imbalance or even a philosophical perspective that, if you try a little, you can empathize with. But I think there also needs to be something truly frightening about them, something unpredictable or an amoral aspect that leaves you feeling uneasy about what they could do at any moment.

I prefer a villain like Magneto from the X-Men franchise, because, though he's the enemy, you totally understand where he's coming from and why he feels the way he does. He's not evil, per se, but he is willing to do whatever he thinks is necessary to bring about the world he envisions for the survival of mutants everywhere.

Snydly Whiplash..

The Brain.

I have to agree with others here who like Heath Ledger's portrayal of the Joker. His is the darkest, most layered version of the villain. It has no camp at all, unlike Nicholson's, who was a good baddie, but still patterned after the Cesar Romero version from the original Batman TV series, right down to the cackle. LOL! Also agree with others here that Ledger's loss was huge.

Yzma from The Emperor's New Groove.

Lex Luther, much like Trump.

I love Jane from the Twilight saga. The book was better than the movie.

Bane as played by Tom Hardy in The Dark Knight Rises
The Joker as played by Heath Ledger in The Dark Knight
The Penguin as played by Robin Lord Taylor on Gotham and Danny Devito in Batman Returns
Loki as played by Tom Hiddleston in the Thor and Avengers series
Agent Smith as played by Hugo Weaving in The Matrix
Hannibal Lecter as played by Anthony Hopkins in Silence of the Lambs
Tommy Devito as played by Joe Pesci in Goodfellas
Cobra Kai Sensei and his students from The Karate Kid
Doomsday
Freddy Krueger
Jason Voorhees
Michael Myers
The Terminator
Gollum (kind of annoying too lol)
Gunnery Sergeant Hartman as played by Lee Ermey in Full Metal Jacket
Leatherface
Megatron
Surtur from Thor: Ragnarok
Hela as played by Cate Blanchett from Thor: Ragnarok was pretty bad ass

I don't know much about the character, but I suppose Thanos will make my list after I see Avengers: Infinity War. He's supposedly one of the top most powerful villains ever.

All of them are either powerful, creepy, diabolical, quirky, assholish, or evil lol. Makes for good entertainment.

Macbeth. In many good stories the hero starts out vulnerable and grows wiser, stronger, and more virtuous as the story progresses. It is the opposite in Macbeth. He starts out as a loyal soldier for his King and devolves into a villain with no qualms about murdering anyone who gets in his way.

Donald Trump and his sidekicks Pence, McConnell, and Ryan. They represent the epitome of evil.

Negan from The Walking Dead! Delightfully diabolical and easy on the eyes

Kevin Spacey's character in Seven.

Wicked Witch from Wizard of Oz . Y'all know...The one with Judy Garland. Yea that witch. Take your pick of East or West.

God

terminator

Real? Probably Kim Jong Whichever. Easy to make fun of, torments and prods the US, bound to die soon.
Fictional? Cobra Commander. Easy to admire, torments and prods the US, bound to take over the world soon.

Anakin Skywalker. All he ever wanted was to save Padme and gain immortality.

Wile E. Coyote.

Look out Bullwinkle!!