Selene was the Goddess of the Moon, and it's personification in Classical Mythology. In many ways, she and her brother Helios took the places of Nyx and Hemera. Helios, Selene, and Eos, were the three siblings who effectively ruled the changing of the hours.
While Selene was driving her milky horses across the sky one evening, her soft gaze fell on the shepherd Endymion. He was taking a nap among all his sheep, and he was one of those guys that is just SOOO cute when he's asleep. So Selene got this huge crush on him. She couldn't get him out of her head.
That night Selene went to Zeus and asked if Endymion could be granted eternal youth and eternal life. She remembered her sister Eos' bad luck with mortal's and eternal life, and had no wish to be left with a grasshopper.
Zeus granted Selene's wish, and Endymion slept on for eternity, smiling in his sleep. And no wonder. He dreamed that he held the moon in his arms, but it was more than a dream, because Selene bore fifty daughters to Endymion - all beautiful, pale, and sleepy.