Hydra

You may be looking for the planet or the specific individual killed by Hercules.

The word "Hydra" was applied to a variety of large, poisonous, snake-like creatures.

One Hydra was a creature that dragged itself across the ground. It had a bulbous body and three eyes, one looking forward, the other two on the sides. Inside the Citadel, Captain Richard Haliwell and Emily Boyes-Dennison were forced to face one of these during one of their tests for survival. Haliwell managed to blind the creature using his cutlass. (PROSE: Imperial Moon ^[+]Loading...["Imperial Moon (novel)"])

Another Hydra fought and killed a lion. Duke Ferdinand obtained some of its venom for Malcome Canker so he could use it to poison Jack Fuller. (PROSE: Minions of the Moon ^[+]Loading...["Minions of the Moon (short story)"])

The Hydra was a creature with nine heads, one of which was immortal, whom the Greek hero Hercules was tasked with slaying. (PROSE: Mythical Monsters ^[+]Loading...["Mythical Monsters (short story)"])