Perseus and Medusa
Before there was Perseus, there was Gilgamesh. Gilgamesh stars in an ancient Sumerian poem called The Epic of Gilgamesh. In one episode, we hear all about how King Gilgamesh (who, like Perseus, is part god) sets off to destroy the evil demi-god, Humbaba. Just like Medusa, Humbaba is beheaded, and his head is stuffed into a sack.
You can read the full Epic of Gilgamesh here.