nemesis

Batman is in constant conflict with his nemesis, The Joker.

“And then, while he's devouring you with his stare, thinking about how much he wants to lick you up, along comes his antithesis, his polar opposite, his nemesis for want of a better word—” “Nemesis?” I interrupted, eyebrows journeying up my forehead. “—who swoops you off your feet and away from him,” Heather continued, ignoring my incredulous expression.

Even Nathan's close associates, who are not yet ready to declare themselves his enemies, accept that his engineered downfall will be his nemesis for harbouring ambitions beyond his status, and do nothing to alert him to the situation[…]