Hrm... looking back over my initial post, I'm not sure I was as clear as I would've liked; what I had in mind was... kind of an Uncanny Valley
version of the Good Doctor
(think that's the trope, anyhow...). Energetic, kind, thoughtful and intelligent... but with a twist to their thinking that removes all hope of any of that being something positive.
Oh, and not that tired old Your Evil Is My Good
thing, either; some kind of real-world mental health issue (that he was intelligent enough to disguise for years until he was in a position to strike back at those who 'tormented' him, and bring their 'reign of terror' down) would work far better for what I was envisioning.