Hydra is a fictional terrorist organization appearing in Marvel movies, TV and comic books. They are a secretive world-wide paramilitary, science and research corporation dedicated to global domination, and frequently in conflict with S.H.I.E.L.D. and The Avengers.
HYDRA is an authoritarian terrorist-criminal-paramilitary organization from the Marvel comics and Cinematic Universe. The organization’s main goal is world domination, going through many different iterations over the years. HYDRA was first built around the worship of Hive, an Inhuman who was banished by his own people to the planet Maveth (where Shield agent Jemma Simmons was trapped in season three of Agents of S.H.I.E.L.D). The cult evolved over centuries into its contemporary form as an extension of the Nazi Party led by Johann Schmidt, who would become the Red Skull.
Hydra was defeated in the Second World War, thanks in part to Captain America and his team of Howling Commandoes, with Red Skull mysteriously disappearing after coming into contact with the Infinity Stone known as the Tesseract.
After the defeat, Hydra’s methods became more insidious as Red Skull’s top scientist, Armin Zola orchestrated a secret section of the organization to spread through the roots of Shield when he was brought to America thanks to Operation Paperclip. While Zola died in the 1970s, his plan would reach fruition decades later as Hydra’s infiltration of Shield was complete. Without the efforts of Captain America, Black Widow, and Falcon, Hydra would have succeeded in its plan to overthrow the world’s governments, replacing them with a fascist empire.
Since Hydra’s defeat, with the Avengers wiping out the last vestiges of the organization, it has managed to rebuild itself many times and still remains a threat in the Marvel Universe.