For some who may not know, it was recently revealed at Comic-Con during the Captain American panel that Hugo Weaving’s character, The Red Skull, works for both the Nazi Party and the HYDRA organization.
But what is the HYDRA organization you ask? Well according to the direct source at Marvel:
Hydra is a world-wide subversive organization dedicated to global domination. At its height, Hydra was the most extensive, powerful, and dangerous such organization in history. Hydra is almost entirely composed of men, with some notable exceptions, such as former member Lara Brown, the daughter of a Supreme Hydra, and so-called Madame Hydra, who later became known as the Viper. Hydra agents wear green costumes with cowls concealing the entire head except for the mouth and chin. Their organization takes its name from the many-headed serpent-like monster known for its ability to grow two heads immediately to replace any head that was severed. Hydra prides itself on its ability to regroup and rebuild itself, allegedly mightier than before, after any major defeat. Indeed, the organization has now endured for four decades.