The Nemean lion was a vicious monster in Greek mythology that lived at Nemea. It was eventually killed by Hercules. It could not be killed with mortal weapons because its golden fur was impervious to attack. Its claws were sharper than mortal swords and could cut through any armor. The lion is usually considered to have been the offspring of Typhon and Echidna.
The first of Hercules' twelve labours, set by King Eurystheus was to slay the Nemean lion. The Nemean lion took women as hostages to its lair in a cave, luring warriors from nearby towns to save the damsel in distress. After entering the cave, the warrior would see the woman (usually feigning injury) and rush to her side. Once he was close, the woman would turn into a lion and kill the warrior, devouring his remains and giving the bones to Hades.
The cave had two entrances, one of which Heracles blocked; he then entered the other. In those dark and close quarters, Heracles stunned the beast with his club and, using his immense strength, strangled it to death. After slaying the lion, he tried to skin it with a knife from his belt, but failed. He then tried sharpening the knife with a stone and even tried with the stone itself. Finally, Athena, noticing the hero's plight, told Heracles to use one of the lion's own claws to skin the pelt.
Being an avid fan of the Percy Jackson series, the Nemean lion is also featured in the books. The lion was sent by Luke and the General at the National Air and Space Museum to stop the group of questing Hunters, demigods, and one Satyr. It battled with Percy, who recognized the monster from the time he saw one from the train during the quest to find Zeus' Master Bolt. The monster was incredibly hard to defeat because of its bulletproof and sword-proof pelt. Percy came up with and idea and grabbed a few packets of astronaut food from the gift shop and tossed it into the lion's mouth when he roared. When the lion bellowed in disgust, Zoë fired arrows into the Nemean Lion's mouth. The lion dissolved except for its pelt. The pelt was offered to Percy by Zoë because it was his plan that made it possible for them to defeat the monster.