Intro. The First Demon: Muzan is the progenitor of all other demons in existence, having become a demon himself over a thousand years ago during the Heian Era.
Demon King: He's known as the Demon King and is the leader of the Twelve Kizuki, the organization comprised of the twelve strongest demons who serve him directly.
Tragic Origin: Muzan was originally a human who suffered from a terminal illness. He underwent an experimental treatment hoping to be cured, which instead turned him into the first demon.
Pursuit of Immortality: His ultimate goal is to conquer the sun and achieve true immortality. He plans to achieve this either by finding the legendary Blue Spider Lily or by creating demons who can withstand sunlight.
Antagonist Role: Muzan is the primary adversary of the Demon Slayer Corps, led by the Ubuyashiki Clan, who are dedicated to eliminating him and all demons. He is also the antagonist in Tanjiro and Nezuko's story, having killed their family and turned Nezuko into a demon.