Derived from Greek Mythology - Book four of The Odyssey, wherein Menelaeus describes to Telemachus how he had heard (after hiding in seal skins and (this is the relevant part) a severely polymorphic - that is, shape-shifting - wrestling match with Proteus aka the Ancient of the Salt Sea, won by holding on regardless of what shape Proteus assumed) (pant pant) that Odysseus was being held captive on the island of Calypso.