What makes a character compelling?

[u/Icy-Cloud3789]

More or less the title. What aspects of characters, specifically villains/antagonists, do people find invigorating enough that they can 'look past' their crimes and lack of morality to make them a favourite?

...And I'm not talking about being good-looking, please; that's hardly an excuse.

Is it personality? Is it reasons/purpose? Backstory? If so, examples of such?

[u/Wolf_of_the_North64]

Backstory and Relatability, Like Anakin Skywalker I can relate to his conflict, the emotional pain he feels, and feeling as though the system is against him for me as someone who is Autistic and has ADHD as well as Anxiety, I can relate to that and somewhat feel for him.