Demon sorcerers as villains are often driven by a single-minded pursuit of power or a cosmic disdain for humanity, which frankly can get a bit boring after a while. They're the final boss lurking in the tower, their motivations reduced to a grand, impersonal evil. I think the most chilling ones, though, are those whose cruelty is deeply personal and intellectual, like Raistlin Majere from the 'Dragonlance' saga before his... evolution. His ambition isn't just to rule; it's to understand everything, to possess all magic, and he views every living thing as a potential component in a spell. That cold, calculating arrogance is far scarier than a demon lord who just wants to burn the world.
When they shift into antihero territory, the core conflict becomes internal. The demonic power or heritage is a curse they constantly battle, a source of strength that threatens to consume their soul. They're often trying to atone for past atrocities or use their 'evil' abilities for a good they themselves don't believe they deserve. Elric of Melniboné is the classic template here—a physically frail emperor sustained by a soul-drinking sword, perpetually revolted by his own nature and the decadent legacy of his people. His tragedy isn't in failing to be good, but in knowing that every step towards a lesser evil still requires a pact with the demonic.
What I find most compelling in modern takes is when the line isn't just blurred but erased. A demon sorcerer antihero might have a perfectly pragmatic, even sympathetic, reason for their actions that just happens to involve blood magic and pacts with unspeakable entities. They're not brooding over their soul; they're making the hard choice everyone else is too 'pure' to make, and the narrative doesn't always punish them for it. That moral ambiguity, where you're rooting for someone who should by all rights be the villain, is where the archetype truly shines.