Muzan Kibutsuji (鬼き舞ぶ辻つじ 無む惨ざん, Kibutsuji Muzan?) is the main antagonist of Demon Slayer: Kimetsu no Yaiba. He is the Demon King, the first of his kind, and 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.