Immortal Bony

Immortal Bony, AKA Koschei the Deathless, is the king of the Underworld in Slavic folklore. Carmen, Tyler, and Gordie are on a quest to discover the identities of all twelve of his daughters.

History
Bony started out as the protagonist of Hans Christian Anderson's The Garden of Paradise, a sallow young man who spent all his time reading books about the Garden of Paradise (Eden). He finally reached Eden only to violate the rules set by the Goddess Fairy, the progenitor of all fairies and current inhabitant of the Garden. She told him that if he gave into temptation and came to her bed when she asked, he would be ejected from the garden, and he did just that. Death then came and made a weird deal where Bony could only go to Heaven if he became a better person and if he did not, he would continue sinking deeper into the ground for all eternity. Carmen, Tyler, and Gordie decide that Bony never tried to become a better person, and so even after he died and turned to bones he lives on forever in his underground kingdom.

An earlier tidbit of his backstory is discovered in Golden Hair, where it was revealed he had all twelve of his daughters while he was still a flesh man before he dried up and became the Bony we know today.

Daughters
At some point in his Immortal life, Bony reencountered the Goddess Fairy, presumably outside of Eden (as he is banned), and they conceived twelve daughters. The daughters are not fairies but have magic in their blood, allowing them to shapeshift and other such things.

They are attracted to the Golden Apples of the Knowledge of Magic and/or Immortality, which their mother stole from the Garden of Eden and spread across the world via Johnny Appleswag.