Doctor Necrosis was a doctor loyal to the Nazis during World War II. At some point in his adult life, he became infected with an illness so-called "white gangrene", a rare and highly communicable disease that caused horrible skin lesions and great pain. Learning that regular blood transfusions prolonged his life, he strove for a cure. He then decided to use his own illness to aid his country while also find a cure for his condition after learning that a rare blood type could cure him.
To this end, he used his credentials to get a job at the Red Cross and by 1944 he was stationed in Brisbane, Australia, where he oversaw the shipment of human blood to the battle fields of the South Pacific. Taking the blood donated by citizens of allied countries, he transfused it into himself and left his own tainted blood in its place. This blood would then infect anyone it was transfused into with white gangrene. During his studies, he learned his assistant Mary Knowles, the daughter of a high ranking military official, had the rare blood type that could possibly cure him.
However, by the time he learned this, his tainted blood scheme was realized by the military who sent Captain America and Bucky to investigate. They arrived in Brisbane and questioned the doctor who did not provide them with any useful information. When Mary passed them a note asking to meet with them, Necrosis ordered his minions to run down the two heroes. When they failed, Necrosis broke up the confrontation and suggested the whole thing was a misunderstanding.
He then returned inside and forced Mary to his operating table to perform to the transfusion to cure himself and infect Mary with the disease. Captain America and Bucky arrived and were subdued by his spies and forced to watch as Necrosis began the operation. However, Cap and Bucky broke free and smashed through the window of the operating theater. During the struggle with Necrosis, the villain dived at Bucky who ducked out the way. Necrosis then landed on a pile of broken glass which pieced his heart, killing him.
Necrosis suffered from an illness he called "white gangrene". It was a highly contagious disease which could be spread through the blood. It caused the skin to become covered with gray blotches and begin to peel, causing great pain. The disease was fatal, but its effects could be slowed with regular blood transfusions that replaced infected blood with a fresh supply. The diseases only known cure was a rare blood type of unknown specification.