Also known as Hesperian Dragon, Ladon was a spawn of Echidna and Typhon. It had one hundred heads as well as one hundred voices. It had a fondness for everything gold, and when Hera becomes annoyed at the daughters of titan Atlas coming to the garden and stealing golden apples, she had no trouble persuading Ladon into guarding the tree which bears the apples.
From then on Ladon was coiled all over the tree, and could keep watch to every direction at once. And when one head would sleep, others would be awake so that surprising the Hesperian Dragon was impossible.
Presumable because of Hera's vindictive nature, Ladon had also secondary task of tormenting titan Atlas, who stood nearby, holding the sky on his shoulders.
Ladon and Heracles
Ladon met it's fate when Heracles was tasked to bring back golden apples from the garden. The beast was slain with bow and arrow that the Greek hero had.
Dragon laid in it's death throes for a long time, and Hesperides were lamenting over the loss of their protector. This attracted Jason and the Argonauts to the garden the very next day, where they witnessed the last moments of Hesperian Dragon.
Zeus admired the fight so much that he raised Ladon to the night sky as the constellation of Draco.