The Hydra was a powerful nine-headed beast from Greek mythology that lived in Lake Lerna near Argos. It had nine heads (human and animal) and was immortal - when one head was cut off, two would grow in its place. She was killed by Heracles when he was on one of his twelve quests.
How did Hercules defeat the hydra ?
Heracles defeated the Hydra in the following way: He decided to use his sword to cut off one of the heads. When he did so, two heads grew in its place. He then turned to his friend Iolaus for help and together they modified the plan. Hercules held the Hydra's heads while Iolaus lubricated them with fire to prevent them from growing. Then Heracles cut off all the heads. They were immortal, but now they could not grow back. Finally, he used his sword to cut off the Hydra's heart - the symbol of its life.