The dude is Gilgamesh who, after finishing his quest to obtain the flower of immortality decides to spend an action in order to recover his stamina and hp, but then a wild snake appears during his nap and proceeds to that eat the flower, so now that snake is immortal.

Oldest lesson in history learned:
If you can’t convince your worth to your DM while obtaining an impossible artifact, the DM will find a way for you to lose that artifact.