Little is known about the origin of Doctor Death, except that his real name is Karl Hellfern, and at some point he decided to put his genius to evil purposes. Doctor Death appeared in the third ever Batman story, written by Gardner Fox, and illustrated by Bob Kane, this means that he has been around longer than Robin.
In Doctor Death's first appearance in Detective Comics #29, he develops a lethal pollen extract and plans to use the poison to extort money from the wealthy with the help of his large East Indian manservant, Jabah. After a confrontation with Batman, Doctor Death seemingly dies in a chemical fire in his lab.
However, Doctor Death reappears in Detective Comics #30. Along with a Cossack named Mikhail, Doctor Death is successful in claiming a victim in his extortion plot, but discovers the man lost his fortune in the Great Depression. He attempts to take a set of diamonds the man had from his wife, but Batman kills Mikhail, foils the plot, and upon catching the doctor, discovers that Doctor Death's face disfigured from the explosion, resulting in a greenish skeletal look. Doctor Death admits he's motivated as much by revenge against Batman as he is by greed.
Bronze Age revival
After decades' of absence, Doctor Death was reintroduced in Batman #345 and Detective Comics #512 . In this updated version, Doctor Death is a paraplegic, but his deadly gas gimmick remains. His assistant is a manservant named Togo.
Modern Age reinventions
Dr. Death had a history with Hush's family business called Elliot Pharmaceuticals while moonlighting as a drug chemist for the Guzzo mob family by cutting heroin. Judson Pierce acquired Dr. Death's services so that his poisons would kill everyone in the hospital that Leslie Thompkins and the Waynes had founded. Fortunately, the plan was not successful and Dr. Death's legitmate holdings were over with and he took his activities further underground from then on. Dr. Death also attempted to spread a deadly toxin through out Gotham, but his scheme was thwarted by the JSA. Doctor Death was revived once again in Batgirl #42-44 and #50. Updated for terrorism awareness, the modern Doctor Death produces biological weapons, selling them on the black market to terrorists and other criminals. He is now a bald, gnome-like man wearing a lab coat and an oxygen mask.
Major Story Arcs
The Batman Meets Doctor Death & The Return of Doctor Death
In his first two appearances (Detective Comics 29 & 30), Doctor Death operates a high-value extortion racket. He threatens wealthy individuals with death if they do not turn over huge sums of money. To that end, he has developed a pollen or pollen extract that is deadly if inhaled. He has also developed an immunity serum which he administers to his henchman. Other revelations in this story arc include the fact that Batman caused a fire that disfigured Doctor Death, that he was financially ruined by the fire, and that he is able to disguise himself convincingly - most notably as pawn broker Ivan Herd.
Batman: War Games
Doctor Death plays a minor role in Batman: War Games, where he is seen working with the Black Mask, releasing a gas into a crowd of panicking gangsters and villains, attempting to wipe out their competition. He is mentioned as one of many mad scientists who have gone missing and is depicted later among other captured scientists and mad geniuses on Oolong Island.
Ministry of Science/ House of Hush
He is later seen working for the New Black Mask , along with the Fright, and Hugo Strange in brainwashing people and raising a new Reaper. After Black Mask's unveiling as Jeremiah Arkham, Dr. Death went back to his old ways of concocting deadly chemicals and diseases. Hush later enlists Dr. Death's help against Batman but soon after Dr, Death is shot by Hush when he proved useless. Dr. Death survived his gunshot wound and released a deadly toxin on Judson Pierce as a form of revenge, before he escaped. The toxin however, destroyed Pierce's cancer, gave him superhuman abilities but it caused his body to become malformed as if he were nothing but skin and bones.
The Death of Doctor Death?
There seems to be a chronological discrepancy regarding the life and death of Dr. Karl Hellfern. Before the New 52 reality, it was implied that Dr. Hellfern was an employee of Elliot Pharmaceuticals and was later enlisted by Hush to exact his revenge on the Batman. In the future of Neo-Gotham, Dr. Hellfern is assumed an alternate identity in order to hide from prying eyes. He was later exposed by Ronald Tagg, a paparazzo who wanted to learn everything Hellfern knew about the weaknesses about all metahumans and superheroes. Hellfern must have refused Tagg's pleas because Hellfern's condo was engulfed by an explosion. Hellfern's smoldering body was eventually found by GCPD.
Now here is where everything is turned upside down by the New 52. Hellfern's life and death takes place in a short time during young Bruce's return to Gotham. Hellfern is now a former employee of Wayne Enterprises and has just developed a formula that can regrow bone loss within the body. However, the formula has devastating side effects. The formula causes the bone structure of the body to harden and grow out of control until the body finally gives out due the skeletal deformation. Hellfern is let go by Wayne Enterprises but then recruited by Riddler in order to help him in his mad plan to take over the city.
Riddler orders Hellfern to inject the forumla into his colleagues who possess crucial information thereby tying up loose ends. Hellfern then injects himself with his formula as a means of a self destructive path. Hellfern had a son who was under Colonel Jake Kane's command. Hellfern pleaded with Kane to keep his son out of danger but it was too late. Hellfern's son died while investigating a possible terrorist cell. A tribe of nomads/ terrorists bobby trapped their lair and Hellfern's son walked into the trap.
Hellfern believed one should harden themselves from any emotion and detach themselves from any moral conventions so they can never feel any pain that life throws at them. Hellfern believed Bruce Wayne had the right idea to leave Gotham after the death of his parents but he is shocked that Bruce decided to come back. Hellfern eventually succumbs to his formula's lethal side effects and dies while leaving young Bruce with the sinking idea that "Should man be an island?"
Justice League Beyond
Hellfern retired his persona as Dr. Death and went into hiding. Unfortunately, the alias that Hellfern went under didn't stay a secret for long. Someone who knew about Hellfern's newfound existence gave it up to Ronald Tagg, a former curator at the Gotham Museum now turned paparazzo. The meeting between Tagg and Hellfern must have not gone well because Hellfern's condo exploded. Hellfern was killed in the explosion and it was believed that Tagg had been killed as well. However, it turns out Tagg had survived because he exposed himself to a chemical that Hellfern was experimenting on. The chemical shared similar properties that transformed Rudy Jones into the Parasite. Tagg must have absorbed the kinetic force of the explosion thanks to the Parasite chemical.