Nigh Invulnerability/Oral Tradition

Examples of in  include:


 * Achilles. According to the Romans, his skin was impenetrable because his mother, a nymph named Thetis, dipped him in the waters of the Styx. His only weak spot was his heel, which didn't touch the water because it was where Thetis was holding him. Of course, this legend leads to a bit of Fridge Logic, even referenced in the movie Troy, as to why Achilles would bother wearing all that armor if that were the case.
 * Achilles is actually depicted as fighting naked in a lot of Greek art... but so are most Greek heroes.
 * The Nemean Lion also had impenetrable skin, according to Pindar and Bacchylides (both c. 480 BCE). The only way Hercules managed to kill it was either choking it or shooting it in the mouth with arrows (depending on the version).
 * Antaeus, the giant wrestler. According to Roman writer Ovid, he could not be defeated as long as he was touching the ground, as he was the son of Gaia, the Earth. Hercules quickly caught on, and finally killed him by holding him above the ground and crushing him to death in his arms.
 * The hero Siegfried from Nibelungenlied and German folk legend became nearly invulnerable by bathing in the blood of a dragon, which made his skin impenetrable (except for a spot on his shoulder).