HYDRA

"Hail, HYDRA! Immortal HYDRA! We shall never be destroyed! Cut off a limb, and two more shall take its place! We serve none but the Master—as the world shall soon serve us! Hail HYDRA!"

- The HYDRA Oath.

HYDRA is a fictional Nazi terrorist organization that appears in the Marvel universe, and they are a major antagonistic faction in the comics.

Marvel Cinematic Universe
In the Marvel Cinematic Universe, HYDRA made their first appearance in Captain America: The First Avenger as major antagonists in this film together with the film's main antagonist Red Skull, their leader and the founder of HYDRA.

HYDRA returned as antagonists in the sequel of The First Avenger which is Captain America: The Winter Soldier and they hide inside SHIELD Agency where they are led by their high-ranking member Alexander Pierce, the primary antagonist, and he and HYDRA used the Winter Soldier as senior henchman and as agent.

Various

 * Red Skull (Founder)
 * Baron Wolfgang von Strucker (Supreme Hydra)
 * Baron Zemo
 * Baron Zemo II
 * Viper (Madame Hydra)
 * Arnim Zola
 * Kingpin
 * Kraken
 * Grim Reaper
 * Silver Fox
 * Fixer
 * Silvermane
 * Richard Fisk
 * Silver Samurai
 * Gorgon
 * Crossbones
 * A.I.M.
 * Norman Osborn

Amalgam version

 * Green Skull (Leader)
 * Baron Zero
 * Madame Cat
 * Nuke
 * Ultra-Metallo
 * Major Zemo

Trivia

 * Though often capitalized, the Hydra organization's name is not an acronym.