The Lernaean Hydra - The second Labor of Hercules

The Hydra was a big snake, a big big snake. It had nine heads. One of its heads was immortal - you couldn't kill it. King Eury made it quite clear that he did not want Hercules returning with any part of the serpent. No snake skin boots or hat or gloves.
King Eury and Hera both knew that anyone who approached the monster's den in the swamp was killed by the monster's poisonous breath. Hercules did not have a chance!
But Hercules lured the monster out of the swamp. With the help of his servant, Iolaus, he clubbed off the monster's nine heads. He burned them. But one head refused to die. It kept coming back to life. So Hercules crushed that head and buried it deep in the ground, and to this day, it was never seen again.