Endymion is a legendary character in Greek mythology; a beautiful youth that spent his life in perpetual sleep because of love. There are variations of the tale, but what remains consistent is his relationship with the eternally beautiful goddess of the moon, Selene.
Selene loved Endymion but was faced with a problem; she was immortal and would retain her youth and good looks forever, but Endymion was a mortal who would age and eventually die.
Selene cast a spell on Endymion, sending him into eternal sleep. In this state of slumber, Endymion would retain his youth.