monster (manga)
A seinen manga series by Urasawa Naoki and published by Shogakukan in Big Comic Original from 1994 to 2001 and later adapted into a 74-episode 2004 anime series by Madhouse.
Dr. Tenma Kenzou was a highly-successful brain surgeon at the Eisler Memorial Hospital in Düsseldorf, East Germany, who was demoted for failing to operate on the city mayor (who later died) in exchange for saving Johan Liebert, a boy who suffered a bullet wound to the head during his parents' murder - only to find out, nine years later, that Johan turned into a psychopathic murderer responsible for the mysterious deaths of his superiors (which unprecedentedly re-promoted him as Head Surgeon). Tenma then went after him together with Johan's twin sister Anna, only to learn horrifying secrets concerning the "monster" he once saved.