What makes a character a compelling bad guy?

I enjoy the character of Marc Remillard from Julian May’s Saga of Pliocene Exile because he is such an overwhelmingly smug character, and yet still affable and relatable — able to be friendly with the protagonists of the story, yet still swan in at the end after having beaten them down with his psionic powers and say “As you can see, I’ve won. We knew I would.” It’s kind of the way I found Lilith relatable in Diablo 4 — sure, she needed to be stopped, but I got where she was coming from.

Meanwhile, I loved Gul’dan not because of any relatable humanizing qualities but rather entirely because he’s pure evil, pure selfish lust for power, and he makes the entire Warcraft continuity work — without Gul’dan’s completely rapacious lust for power and self aggrandizement, you don’t get half of what makes Warcraft fun. You don’t get to watch an entire people swayed by the lies of someone who knows what he’s doing will lead to their ruin and who does not care — someone who would gleefully plunge every Orc in existence into a festering pool of demon blood and fuse them all together into a giant battle monster for even one more second of his own depraved existence.

Sometimes I like to feel like a villain is relatable, and sometimes I really just want to hate their guts.

But what about you guys? Do you love Arthas Menethil for his evil deeds as the Lich King, for his struggles as a young prince trying to save his kingdom and finding himself chasing after a Nathrezim, or the way he seemed to be constantly at odds with his own existence? Did Deathwing work for you as a giant kaiju, or did you wish he’d made a return as the smarmy politician of the Day of the Dragon novel? What makes a bad guy one that you want to see around?