Hydra, also known as Mother Hydra, is a creature which which features in H.P. Lovecraft’s Cthulhu Mythos.
Said to resemble a colossal Deep One, Mother Hydra is an enormous humanoid creature with a fish-like face, flapping gills and piscean skin. She, along with Father Dagon and Great Cthulhu himself, form the “holy trinity“ of the Deep Ones: the three entities worshiped as gods by that aquatic race.
There is much debate on whether Mother Hydra is a Great Old One herself, or if she is simply a massively overgrown Deep One (considering that some Deep Ones continue to grow as they age), but it should be noted that Hydra and her consort Dagon have been entrusted by Cthulhu with the guardianship of his “daughter” Cthylla. This is a duty which they perform in one of the Deep Ones’ mighty submarine cities somewhere beneath the North Atlantic.
Mother Hydra was one of the Wilmarth Foundations‘ targets during Project X in March of 1980. The operation was ultimately unsuccessful, and she was able to escape the partial destruction of the Deep One city outside Innsmouth harbour, along with Father Dagon and Cthylla.