Princess Eilonwy was a human being.
Born in Prydain in the Dark Ages, the Princess Eilonwy was a clever, well-mannered and brave young girl when she was kidnapped by the Horned King, who hoped her Bauble could help him find the Black Cauldron somehow. When that scheme failed, the King unceremoniously kicked her into a dungeon, from which she had no trouble escaping on her own powers. On the way, she freed the young, would-be-heroic pig-keeper Taran and the bard Fflewddur Fflam, who would go on to become her friends, along with Gurgi. Eilonwy was instrumental in the defeat of the Horned King, and continued to go on various adventures with the others, having moved to Caer Dallben. As they grew up, Eilonwy and Taran fell in love, and eventually married.