Looking for philosophy books to help write ideological conflicts in fantasy

I’m a beginner writer aiming to create an epic action-adventure fantasy. I have most elements of the worldbuilding figured out, but I struggle with crafting compelling characters and meaningful conflicts. I want my antagonist to be deeply philosophical—not edgy, not purely evil, but rational and principled, with an ideology that readers could genuinely sympathize with or even agree with.

Could you recommend philosophy/related books that would help me develop that kind of characters and antagonist?