Hydra
Famous for being one of the 12 Labors of Heracles, the defeat of the Hydra (otherwise known as the Lernean Hydra in Greek legend) seemed an almost impossible feat. This nine headed (although the number varies) gigantic water-snake-like monster would inhabit the marshes of Lerna, near Árgos. Considered an almost indestructible foe due to the fact that every time you cut one of its heads off, two would emerge from the wound. If that wasn’t terrifying enough, one of it’s heads happen to be immortal.
According to the early Greek poet Hesiod’s Theogony, the Lernean Hydra was the progeny of the monstrous serpentine giant Typhon and the half-woman and half-snake like creature Echidna. He would finally be defeated by Heracles ingenuity, when he enlisted the help of his nephew Iolaus. As Heracles hacked off each of the mortal heads, his nephew would use a torch to cauterize the fresh wounds, stopping the heads from regrowing. When only the last head remained, the immortal one, Heracles lopped and buried it under a heavy rock on the sacred way between Lerna and Elaius.
Learn more about Heracles defeat of the Hydra and his other labors here