Lamia

Lamia is an ancient demonic creature originating from Greek mythology. According to legend, this daemon was once a beautiful queen who ruled over Libya. Zeus, king of Olympus, was so intoxicated by her beauty that he took her as one of his many consorts. This caused his wife Hera to become jealous and, in her rage, she kills Lamia's children and transforms Lamia herself into a monster who is cursed to feed on the blood of children.

Description
In the original legend, Lamia was a woman of fantastic beauty until she was cursed by Hera. Her once glamorous visage was twisted to horrific ugliness to fit her newfound craving for children's blood, but she more or less retained a human form. She was, however, renowned for wearing a skirt of snakeskin that covered her legs.

Another common interpretation of Lamia is that of a human-snake hybrid. She retains a humanoid head, upper body and arms, but below her waist is a long serpent's tail. This description originates from the 1819 poem Lamia written by John Keats and has been popularized in modern fantasy media. Lamia's habit of feeding on human blood is also a trait shared by other popular monsters such as succubi and vampires.