Hydra

In Greek mythology, the Lernaean Hydra was an ancient nameless serpent-like chthonic water beast that possessed numerous heads and poisonous breath

The Hydra of Lerna was killed by Hercules as one of his Twelve Labours. Its lair was the lake of Lerna in the Argolid, Beneath the waters was an entrance to the Underworld, and the Hydra was its guardian