Retsu UNOHANA

Unohana is a soft-spoken, polite, and caring woman and is the captain of the 4th Division. She uses honorifics when addressing everyone, including her subordinates, and rarely shows panic or distress. She is even polite when angry (for instance, when members of other divisions bully her division), maintaining her smiling demeanor while radiating a dangerous aura that immediately scares others away. She wears the standard shinigami captain uniform, but wears an obi instead of the normal one, and her hair is worn braided over her chest. Presumably the longest serving captain after Kyouraku and Ukitake, Unohana has a presence that tends make everyone around her feel at ease. However, her anger is just as potent as even members of 11th squad become paralyzed with fear whenever they’re careless enough to invoke her wrath. In omake chapters and scenes, it is shown that Unohana has a curiosity about convenience stores in the world of the living, and also likes picking racy swimsuits for Isane when she visits the living world.
Unohana is the original “Kenpachi” (a name given to the strongest shinigami). Although she now goes by Unohana Retsu, her name is actually Unohana Yachiru.
Unohana was the founder of 11th division and its first captain. Before joining the Gotei 13, she was the most diabolical criminal to ever exist in Soul Society.
At some point in time Unohana was taught healing techniques by Kirinji Tenjirou.