Doctor Death (Dr. Karl Hellfern) is historically the first super-villain encountered by Batman. He has been reinterpreted several times throughout the series.
In his first appearance in Detective Comics #29, Doctor Death develops a lethal chemical agent from pollen extract and enacts a plan to use the poison to extort money from wealthy Gotham City citizens. He is assisted by a large East Indian manservant, Jabah. In an attempt to evade capture by Batman, Doctor Death ignites chemicals in his laboratory, presumably killing Jabah and himself in the resulting explosion. Doctor Death next appears the following month in Detective Comics #30. With a new accomplice, a Cossack named Mikhail, Doctor Death is this time successful in claiming a victim in his extortion scheme, but discovers that the poisoned man lost his fortune in the Depression. Batman intervenes in the plot and upon apprehending the doctor, discovers that Doctor Death's face is horribly disfigured from the lab explosion, resulting in a brown, skeletal appearance.
The scriptwriter for Detective Comics #29 and 30 is an issue of dispute, leaving the creator of Doctor Death uncertain. Batman creator Bob Kane is officially credited as scriptwriter of these issues, while "authorship was claimed years later by Gardner Fox," scriptwriter of Detective Comics #31 and 32.
Bronze Age revival
After several decades' absence, Doctor Death was reintroduced by writer Gerry Conway in Batman #345 and Detective Comics #512 (1982). Conway's story is an update of the original 1939 tale. In this version, Doctor Death is depicted as a paraplegic, but his deadly gas gimmick remains the same. He is assisted this time by a manservant named Togo.
Doctor Death was revived once again in Batgirl #42-44 and #50 (2003-2004) by writer Dylan Horrocks. His history is again slightly altered: Updated for an era of increased terrorism awareness, the modern Doctor Death is a producer of biological weapons, often selling them on the black market to terrorists and other criminals. He is now depicted as a bald, gnome-like man wearing a lab coat and an oxygen mask.
This incarnation of Doctor Death plays a minor role in Batman: War Games, Act Three where he is seen working with the crime lord Black Mask, releasing a gas into a crowd of panicking gangsters. Batman suspects that he and Black Mask are attempting to wipe out their competition.
Doctor Death remains active in the DC Universe following the events of Infinite Crisis. In the second issue of 52, he is mentioned as one of many mad scientists who have gone missing. He is depicted later in the series among other captured scientists and mad geniuses on Oolong Island.
Other Doctors Death at DC Comics
A different character named Doctor Death appears in Doom Patrol (Vol. 1) #107 (November 1966). In a story set in 1939, Wesley Dodds encounters a serial killer named "Dr. Death" in Sandman Mystery Theatre #21 (December 1994). This Dr. Death was responsible for euthanizing his elderly patients.
In Batman: The Animated Series, on the episode "Beware The Gray Ghost," Simon Trent's Gray Ghost episode collection features one episode called "Dr. Death."