The Hydra was created by Norman Osborn from DNA he had stolen from S.H.I.E.L.D. files relating to Ulluxy'l Kwan Tae Syn. With the intention of using the threat of Hydra, and his knowledge of how to stop it, as a means to establish his own place within the power structure of the government, Osborn released the Hydra into New York City where most of the city's population was assimilated into the Hydra collective within hours.
When Captain America refused to aid Osborn in his duplicitous attempts in battling the Hydra, Osborn had the Hydra kill and absorb most of Captain America's closest friends and allies, including several Avengers and S.H.I.E.L.D. agents. Of those it absorbed, it chose the re-animated corpse of She-Hulk to become the "Hydra Queen"; the body representative of the collective as a whole.
Osborn turned to Tony Stark who, unlike Captain America, agreed to join forces with Osborn to stop Hydra. Creating the Iron Avengers, a group of robots based upon the Avengers, Osborn and Stark seemingly killed most of the Hydra collective and forced the remnants to retreat.
The Hydra was created by Alex Ross, Jim Krueger and John Paul Leon and first appeared in Earth X #1.
Major Story Arcs
For more information see: Universe X
Embarking on a quest to destroy Death with the reborn Captain Marvel, Captain America found himself again facing The Hydra when he and Mar-Vell needed to obtain the Nega-Bands worn by Rick Jones, whose re-animated corpse was a part of The Hydra. Upon finding Rick Jones' reanimated corpse, Captain America became infuriated to see his friend being used by The Hydra and came to the realization that he and all others absorbed in the Hydra are truly dead.
Attacking the Hydra in a furious rage over the acceptance of the demise of most of his closest friends, Captain America freed most of his friends bodies from the Hydra and then destroyed the Hydra once and for all with Rom's Neutralizer.
Powers and Abilities
The Hydra could reanimated dead bodies as part of it's collective with it's own will now that of it's victims. The Hydra controlled hundreds of bodies meaning it's reach was vast in scope and it's only real motive was continuing to extend it's numbers. The Hydra would often manipulate people to willing join the collective but also would force itself onto those who resisted.