Spoiler for like, any book existing.
I think mine has to be the villain in Mirror Man. Idk, he wasn’t intimidating, he wasn’t interesting. He was meh.
Also the villains from The Chain. Dear God they weren’t sympathetic in the slightest. The book tries to act like they were atleast pitiful but FROM THEIR INCEPTION, they were just evil assholes who enjoyed causing pain. The book itself wasn’t all that great anyways.
Atlas au Raa from the later Red Rising books.
He’s pretty much space Vlad the Impaler but worse.
I came here to say this. Pretty much every atrocity that occurs since the Rising was his doing.
Every time the fear knight shows up on page you know something absolutely fucked up is gonna happen, like >!taking Tharsus, chopping his hands and feet off in zero g, crushing his bones, putting a bowl over his head to preserve it as a trophy, then throwing him, alive, into a cage to be eaten by a manticore. All without hesitating one second, like it is second nature for him.!< (spoilers Light Bringer)
The Fear Knight made me mad, for sure, but fucking Lysander. He’s my answer to this question.