Mr. Hartmann worked in Kinderheim 511, due to his high-level position in the East German Ministry of Health. Tenma contacted him in order to gain more information about the orphanage and the origin of Johan Liebert. Hartmann was intrigued by Johan's intelligence and his way of manipulating, this led him to make a "monster" of Dieter, a child he was taking care of. In hope to make Dieter more resembling to Johan, Hartmann physically abused Dieter. Tenma discovered the bruises all over Dieter's body and took him to the hospital. Tenma was able to convince Dieter to leave Hartmann for his good.
In Another Monster, it is revealed that he was arrested.
Hartmann at first seems to be a kind and caring man. However he is a soon revealed to be a sociopathic and deranged man with an unhealthy obsession with Johan, going as far as to attempt to create “clones” he was eventually arrested on grounds of child abuse as revealed on Another Monster.