HYDRA , occasionally referred to as the Thule Society, was born as a Nazi deep science organization during the second World War, the child of two organizations- the Brotherhood of the Spear and the Brotherhood of the Shield, which were nearly destroyed when their discoveries caused The Brood to attack them. Shortly after their founding, HYDRA began to spread out to get involved in every facet of modern human living- science, medicine, history and literature were all tools for the organization to wield. When World War II broke out, HYDRA devoted most of its resources towards the investiagtion of the occult to create new weapons and mystic powers for Adolph Hitler. During this time period, the illustrious Baron Wolfgang von Strucker lead the organization, and while he had a great deal of ambition, he was frequently thwarted by the efforts of Captain America and The Invaders, as well as Sergeant Nick Fury and his Howling Commandos. Despite these frequent disgraces, Strucker's time in charge of HYDRA lead to the discovery of Asgard, which allowed the Nazis to recruit Thor to their side for a brief period of time as well as unleashing horrific monsters from the other realms on their foes, and they made great strides in weapons technology which would have created an arms race if the allies didn't have Howard Stark's own engineering genius on their side.
While it has never been as strong as it was during the second World War, HYDRA has perservered for decades, and continues to strike fear into the hearts of many who oppose them. They are currently lead by Ophelia Sarkissian- codenamed Madame Hydra or Viper. They continue to clash frequently with supervillains of many types, and are believed to be building up their forces in larger numbers at bases in Bavaria, New York and Moscow, as well as their own personal flying HYDRA Island.