Hydra in Wikipedia
In Greek mythology, the Lernaean Hydra (Greek: Λερναία Ὕδρα
(help·info)) was an ancient nameless serpent-like chthonic
water beast (as its name evinces) that possessed seven heads -
and for each head cut off it grew two more - and poisonous
breath so virulent even her tracks were deadly. The Hydra
of Lerna was killed by Hercules as one of his Twelve Labours.
Its lair was the lake of Lerna in the Argolid, though
archaeology has borne out the myth that the sacred site was
older even than the Mycenaean city of Argos since Lerna was
the site of the myth of the Danaids. Beneath the waters was an
entrance to the Underworld, and the Hydra was its guardian.
The Hydra was the offspring of Typhon and Echidna (Theogony,
313), both of whom were noisome offspring of the earth goddess