Who are the most terrifying villains that you’ve read in Fantasy?

I’m not looking for morally grey or nuanced villains, simply a villain who is actively scary and stays in your mind after you finish the book. A lot of the fantasy I read have either incompetent villains, big bad force of nature who doesn’t really have any distinguishing traits, infuriating and annoying villains, or no villain at all (both sides of the conflict being equally bad).

The closest I’ve got to a villain who actually feels intimidating and capable is Bayaz in First Law- but thats only towards the end of the third book.

I would especially like recommendations for some lesser known books with this.