Inojin Yamanaka

Mayuri kurotsuchi is a major character in bleach. He is the current captain of squad 12th division of the gotei 13 and overseer of the soul reapers research and development institute.

History
110 years ago, Mayuri Kurotsuchi was an inmate in the Maggots Nest, the only one dangerous enough to be chained behind bars for his utter lack of regard for the life when it comes to experimentation. But that changed when Mayuri is visited by Kisuke Urahara and his lieutenant Hiyori Sarugaki, the former offering Mayuri a position in the SRDI. After initially refusing being Urahara's assistant, Mayuri accepts when Urahara points out that he be his successor should anything happen to him. Nine years after his release, Mayuri becomes the new captain of Squad 12 after Kisuke and Hiyori left the Soul Society, creating Nemu Kurotsuchi to be his lieutenant and lab assistant. During this time, Mayuri experimented on Quincies, including Soken Ishida, the grandfather and trainer of Uryū Ishida.

Personality
Mayuri is a pure sociopath, seeing everyone as a test subject to expirement on, this includes himself, he is a very sadistic and downright destructive psycho who has little to no regard for any life. He's often seen laughing or taunting every one of his oppenents, his sociopathy exceeds even that of kenpachi zaraki and byakuchi Kuching. Despite this, he has shown some sense of morality, he openly despises both sosuke Aiken and Szayel Aporro Granz and even went out of his way to fight them off, and while he has no regrets for the things he's done, hid expirements have undeniably helped out and have saved people, despite how immoral they may be.