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. 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.