Muzan Kibutsuji

Muzan Kibutsuji is the main antagonist of Demon Slayer: Kimetsu no Yaiba.

He is the progenitor of all demons in the series — the very first demon and the one who can create others by giving them his blood.

Key characteristics:

• Extremely pale skin, sharp crimson eyes with slit pupils, and black hair (often appears with a white fedora and formal Western-style clothing in his human disguises)
• Possesses an almost god-like level of power among demons: immense strength, speed, regeneration (to the point of near-invulnerability), and the ability to alter his body in grotesque and lethal ways
• Can kill demons remotely with a mere thought if they displease or threaten to expose him
• Ruthlessly intelligent, narcissistic, and paranoid — he is obsessed with overcoming his one weakness (sunlight) and has spent a thousand years searching for a way to become a perfect immortal being
• Views humans and even most demons as disposable tools or inferior beings

Despite his elegant and refined appearance when disguised as a human, his true personality is cold, cruel, and utterly merciless. He is widely feared and despised even by the demons who serve him (the Twelve Kizuki), as he rules through absolute terror rather than loyalty.

In short: Muzan is the ancient, supremely powerful, and deeply malevolent demon king at the center of the entire conflict in Demon Slayer.