Muzan Kibutsuji

Muzan Kibutsuji is the main antagonist of Demon Slayer: Kimetsu no Yaiba. He is the Demon King, the first of his kind, as well as the progenitor of all other demons in existence. Muzan is also the leader of the Twelve Kizuki, an organization of the twelve strongest demons in existence that serve directly under him. A millennium ago, during the Heian Era, Muzan was turned into a demon during an experimental treatment trying to cure his terminal illness, and his goal since then was to live without the fear of death and become truly eternal.