Mayuri Kurotsuchi

Mayuri Kurotsuchi is the captain of the 12th Division in the Gotei 13 and the president of the Shinigami Research and Development Institute in Bleach.

He is widely regarded as one of the most brilliant, twisted, and morally unhinged scientists in the Soul Society. Mayuri is a mad scientist archetype taken to the extreme: he has almost no ethical boundaries, performs horrific experiments on both living and dead subjects (including other Shinigami), modifies his own body extensively with mechanical and biological augmentations, and views everyone around him primarily as potential test material.

Appearance: Distinctive look with golden teeth, white face paint resembling a kabuki actor or skull, colorful modified captain's haori over normal shihakushō, and a strange hat-like headdress. He often has a hunched posture and a perpetually smug, condescending expression.

Personality: Extremely arrogant, sadistic, sarcastic, and brutally honest. He shows almost no empathy or concern for others unless it serves his scientific curiosity. Despite his repulsive traits, he is undeniably a genius inventor and tactician who has created many of the most advanced technologies and zanpakutō modifications in the series.

Zanpakutō: Ashisogi Jizō (a poison-based blade that can paralyze or kill with its venom and has a Bankai form resembling a giant grotesque baby creature).

In short, Mayuri is the quintessential "evil genius" of Bleach — hated by most characters, feared for his unpredictability, but respected (begrudgingly) for his unmatched intellect and contributions to Shinigami technology.