Sigma

Sigma is the primary antagonist of the Mega Man X series. Once the commander of the Maverick Hunters, Sigma fell into insanity and turned Maverick himself, becoming the leader of all haywire Reploids in waging war on humanity. Although he has been destroyed countless times, Sigma's programming almost always survives and finds a new form, ready to menace the world once again.

He serves as the final boss in all mainline games in the series, except Mega Man X8 where he is the penultimate boss in Normal and Hard mode.