Hive is a recurring villain in the Marvel Universe, first debuting in the Secret Warriors comics. He is a parasitic organism that was bio-engineered to physically embody the idealism of HYDRA, therefore becoming one of the organization's leaders.
Created in the HYDRA laboratories in their home base of Gehenna, the Hive was an experiment made to physically embody the HYDRA ideal. The entity is composed of untold numbers of genetically-engineered parasites. An unknown and unwitting HYDRA agent was offered/fed to these parasites as a host around which they could merge into a singular being. Grotesque and menacing in both stature and appearance the Hive had no identity of its own, as its collective will dominates the human host it engulfs; however, it possesses a quiet and cunning intelligence and as a result of its conditioning is completely dedicated to the HYDRA cause to the extent that Baron Strucker appointed it as a figurehead alongside himself, the Viper, Gorgon, Kraken, and the new Madame Hydra, Valentina Allegra de Fontaine.
When HYDRA went to war against a rival organisation, Leviathan, Valentina revealed her true allegiance and murdered her predecessor, the Viper. When von Strucker and the other heads discovered her corpse, the Hive shocked and appalled them all by merging with the deceased woman's body -- re-animating her, but with the parasites themselves gathering into a bulbous mass atop her head with four prehensile tentacles.
Taking back her title as Madame Hydra, she and Gorgon subsequently broke away from von Strucker's weakening grip on HYDRA and formed an alliance with the recently escaped Norman Osborn and his H.A.M.M.E.R. organization. During this brief and fragile union, Osborn arranged for Madame Hydra to undergo surgery to remove the Hive from her in a way that would keep her alive.
Hive was tracked down and found alive years later by the new Madame Hydra, Elisa Sinclair, in an ancient HYDRA temple in Egypt, and had it become a member of the new High Council of HYDRA she was gathering.
A version of Hive (also known as Alveus) appears in the TV series, Marvel's Agents of S.H.I.E.L.D. He is the main antagonist of Season 3. He is an ancient parasitic Inhuman who can possess dead humans as hosts, consume living human flesh and mind control other Inhumans. After being banished to another planet, his powers influenced the foundation of HYDRA. He is primarily portrayed by Brett Dalton, who previously portrayed Grant Ward, whom Hive possesses after his death.