In Greek mythology, the Lernaean Hydra was a terrifying, multi-headed serpentine water monster that guarded an entrance to the Underworld at the lake of Lerna. Famously killed by the hero Heracles (Hercules) as the second of his Twelve Labors, the creature is legendary for its ability to regenerate. Sent by King Eurystheus to slay the beast, Heracles quickly realized that brute force alone would fail because of the multiplying heads. To defeat it, he enlisted the help of his faithful nephew, Iolaus. As Heracles severed each mortal head, Iolaus used a firebrand to cauterize the raw neck stumps, scorching them shut so new heads could not sprout. The goddess Hera, who hated Heracles, even sent a giant crab named Cancer to distract the hero during the fight, but Heracles easily crushed it underfoot. Once only the final immortal head remained, Heracles chopped it off and buried it deep underground beneath a massive rock to trap its power forever.