Dr. Arnim Zola was a Nazi biochemist during WWII. Zola created a virus, that was to be Hitler's doomsday weapon, however the allies took down Hydra, before they could unleash it.
After the war, Zola spent 30 years at Spandau Prison. When he got out he disappeared from the face of the Earth for years, until Interpol discovered him and Zola was handed over to S.H.I.E.L.D.
Hydra eventually got their hands on him and Zola was able to recreate the virus. He was ultimately killed when he tried to kill Nick Fury, using Fury's own gun (which had been designed to only allow Fury to use it, while taking out anyone else who'd try to use it).