Jung Ba Reum (in Korean: 정바름) is the villain protagonist of the South Korean TV series Mouse. He is a rookie police officer by day and a manipulative, sadistic serial killer by night. On the surface, Jung Ba Reum is an extremely kind and well-meaning man. This soft exterior makes him the target of mockery and criticism. Indeed, his goodness sometimes borders on naiveté or incompetence. He comes across as weak and sensitive: someone who has a hard time stomaching the sight of dead cats, let alone dead bodies. As a result, fellow officers and neighbors alike are convinced he is harmless. To them, he is the epitome of the boy-next-door. In reality, every kind gesture is calculated, every altruistic act carefully planned to craft a facade of agreeable neighbor or colleague. His cunning nature is best illustrated when he purposefully waits for Ko Moo Chi's car to be near before squatting down to "rescue" a bird. Ba Reum's true colors show when no one is looking. He is cold, unfeeling, cruel. His personality appears much closer to the one he had as a child, while living under the name Jae Hoon. However, he shows more affect as an adult and seems to feel genuine pleasure, laughter and excitement as he commits his evil deeds. After receiving a graft of Sung Yo Han’s brain, Jung Ba Reum still experiences sadistic urges but he also has access to a wide range of emotions he couldn't experience before: guilt, protectiveness, pain, love... His demeanor grows more confident as part of his memory is gone and his reason for acting meek is forgotten. Due to the traumatic brain injury he suffered, he initially does not remember his past actions in season 2 and is troubled by the homicidal thoughts he is dealing with. His compassion and emotions are authentic. While he still is an opportunistic killer, he now wrestles with a conscience and all kinds of moral considerations. He has to act under the guise of vigilantism to make his crimes feel justified.