When does a villain become likeable as the villain to you?

And I'm not talking some small time villains(who cause some silly harm and then befriend the mc the next day) or just the ones that act similar to rivals, I'm talking about characters that are THE THREAT in the story with the most insane and crazy plans they execute and are ruthless too at times.

Personally, if the said villains have a strong motive with equally strong backstory to support the motive, I'm pretty sold on them, also bonus point if their presence can be felt before their official introduction or even after their defeat.

I feel like this could be the only reason but I'd love to hear if there could be other reasons, doesn't matter if it's just a personal opinions, I don't judge.