The first of Heracles' twelve labors was to slay the Nemean Lion and bring back its skin.
Heracles defeated the beast by throttling it with his bare hands because its skin was so thick that using his bow-and-arrow, a club made from an olive tree he pulled out of the ground himself and a bronze sword were all ineffective. Heracles spent hours trying to skin the lion unsuccessfully, and gradually growing angrier as it appeared he would be unable to complete his first task. Eventually Athene, in the guise of an old crone, helped Heracles to realise that the best tool to cut the hide were the creature's own claws and so with a little divine intervention he completed his first task.
From that moment forth he wore the impenetrable hide as armour, and Eurystheus was so frightened by Heracles' fearsome guise that he hid in a bronze jar and from that moment forth all labours were communicated to Heracles through a herald.