The Nemean Lion was a legendary creature in Greek mythology that ravaged the area of Nemea. Its fur was impenetrable by the weapons of humans and hence, was unstoppable. It was considered to be the child of Typhon and Echidna, father and mother of all monsters. Other accounts mention Zeus and Selene as its parents.
Slaying the Nemean Lion was the first task that King Eurystheus asked of the demigod Heracles during the myth of the Labours of Heracles. One version has it that the lion kidnapped women from Nemea and kept them in its lair, in order to lure warriors. When the brave warrior would see the woman, she would turn into a lion and kill him. Heracles reached a nearby city, where he met a young boy; the boy told him that if he killed the lion within thirty days, then a lion would be sacrificed to Zeus. Otherwise, the boy would sacrifice himself.
Heracles tracked down the lion and tried to kill it by shooting arrows. He realised though that it was no use because of its impenetrable fur. He then waited until the lion entered its lair from one of the two entrances. He then blocked off the second entrance, and entered the cave as well. There, he managed to kill the lion by strangling it with his bare hands. He then tried to remove the skin from the lion but his knife was unable to cut it. After a lot of effort, the goddess Athena decided to help him, and told him to use one of the lion's claws to skin the creature. Heracles emerged victorious on the thirtieth day after he had met the boy.