The Hydra was a many-headed monster in Greek mythology. It was incredibly difficult to kill, because whenever one of its heads was cut off, two more would spring up from the stump. The hydra was eventually defeated by Hercules as one of his twelve tasks.
Hydra originally possessed nine heads, but two new heads grew in the place of each one that was decapitated. If a flaming brand was placed on a wounded head, it would not grow back. The center head was immortal and was defeated by being placed under a boulder.
- The Hydra is such an enduring mythological figure that the term “hydra” is sometimes used to describe a challenge which seems to keep getting bigger and harder to handle, no matter how hard someone tries to metaphorically behead it.