Hydra

Hydra lived in the swamps near the city of Lerna (in Argolida) and destroyed its surroundings. But nobody could do anything about it, because one of its heads was immortal and the others grew back (if someone cut off another head, it grew two more).

Hydra was only defeated by the hero Herakles, who was given the task by King Eurystheus. He was assisted in this task by Ioláos, and this was because Hydra also had a helper - a giant crayfish. Heracles set fire to the forest beyond the Lernaean marshes to prevent Hydra from retreating. And then he began to fire arrows at Hydra. As soon as Hydra attacked him, he cut off her head, but it grew two more. At that moment, a giant crab bit into Heracles' leg, but Ioláos defused it. After the dead crayfish, Hydra looked back, which Herakles took advantage of, tore out a burning tree and burned its head so that no new head appeared. He dealt with the other heads in the same way, including the immortal one. He chopped up the body of the dead Hydra and buried it deep in the ground. He used Hydra's bile to cloud his arrows, for the wounds caused by them were incurable.

Hydra had several siblings, who were Orthos (a two-headed dog), Kerberos (a three-headed dog, guardian of the realm of the dead), Sphinx (a monster with the head and chest of a naked woman, the body of a lion, a serpent's tail with eagle's wings), and Chimera (a monster with the body of a lion, the middle of a goat, the back of a dragon, breathing fire with three mouths).