King Muzan is the powerful King of all the Demons, who has the ability to inject his victims with blood that allows him to convert them into more Demons. He uses this to procreate his abyssal race in order to replace humanity as the dominant species on the planet.

Originally a human, Muzan suffered from a terminal illness, during an experimental treatment, Muzan became the first ever demon. He is also the progenitor of most other Demons and the leader of the Twelve Kizuki. 