Selene the moon goddess was a minor figure in ancient Greek mythology. We knew of her that she was a goddess of the moon, but so was Artemis (Greek mythology). Most mythologists assumed that Selene was an older moon goddess that was replaced later by Artemis in myth.
The only other significant story mentioning Selene in ancient Greek mythology is that of the Nemean Lion, whom it is said that Selene had great affection for. In more modern myth, Selene is found to be associated with the origin of Vampire mythology. In this respect she returns to her role as a moon goddess.
Before she was Selene The Moon Goddess, she was a simple human woman named Selene who worked at the Temple of Apollo in Delphi. It is believed that her sister was the Pythia, or Oracle, of the temple. Either way, Selene worked as a Maiden of the Temple, who assisted the Oracle and cared for the temple. Selene was a worshiper of Apollo (Greek mythology), the sun god, originally, until he cursed her true love, Ambrogio, who eventually became the first vampire.
The couple was given protection by Apollo's sister Artemis, the moon goddess, and they moved to Ephesus to worship and serve Artemis at her famous temple there.
Ambrogio was immortal and did not age, but Selene was still mortal and eventually became older and presumably sick. In exchange for their protection, Artemis insisted that the couple could never touch (Artemis was a virgin goddess and all of her closest followers were virgins as well). Therefore the couple never had children.
On Selene's deathbed, Artemis allowed Ambrogio, now a vampire, to drink Selene's blood. Their combined blood could create their "children" after Selene's death, essentially turning any human who drank the blood into a vampire.
Selene died and Artemis made her an immortal goddess of the moon. Specifically, "Selene the moon goddess" is actually "Selene the moonlight goddess". Selene is the personification of the moonlight that finds its way to Earth. In this form, she can finally touch her husband and children.