Lernaean Hydra
Dragons in Greek mythology often guard treasure. For example, Ladon, a hundred-headed dragon, guarded the tree of Hesperides until he was slain by Heracles. Likewise, Python guarded the oracle of Delphi until he was slain by Apollo out of revenge for Python tormenting his mother. The Lernaean Hydra, a multiple-headed serpentine swamp monster killed by Heracles, is said to be a dragon.