Karl Helfern was the mad scientist who was often known as the first official "Supervillain" of Gotham City, being one of the costumed criminals inspired by the Red Hood Gang. He was the first Metahuman that the Batman faced off against and the second major villain after Red Hood One. Due to his "serum of death", Helfern had a skeletal appearance, giving him the moniker of Dr. Death.
A scientist at Wayne Enterprises, Karl Helfern believed himself a friend of Lucius Fox and the Wayne Family. This all changed after Helfern's son died searching for Bruce Wayne in Nigeria. After the board found out about Helfern's serum of death, even Fox voted for Helfern to be removed from the company. Disgruntled, Helfern tested the serum on himself, becoming a Metahuman monster. Afterwards, Helfern managed to perfect the serum, allowing it to kill several people by causing uncontrolled bone growth. Allying himself with the Riddler, a fellow criminal and former Wayne Enterprises employee, Helfern became Dr. Death and began using his serum to kill and secretly take machinery needed for a doomsday device. During this time, Helfern encountered the returning Bruce Wayne and attempted to kill him. Death later waited at Riddler's weather balloon to guard the doomsday device. There he fought the Batman, but was hit by a piece of shrapnel, causing his bones to greatly mutate and for him to die shortly thereafter.