|“||You, my dear, have the makings of a sorceress. Like me.||”|
Circe's parents were Helios, the Titan of the Sun, and Hecate, the goddess of magic. Circe transformed her enemies, or those who offended her, into animals through the use of potions. She was renowned for her knowledge of drugs and herbs. Circe also purified the Argonauts for the death of Apsyrtus, as related in Argonautica, may reflect early tradition. In Homer's Odyssey, banished by the gods, Circe is described as living in a mansion that stands in the middle of a clearing in a dense wood. Around the house prowled strangely docile lions and wolves, the drugged victims of her magic; they were not dangerous, and fawned on all newcomers. Circe worked at a huge loom. She invited Odysseus' crew to a feast of familiar food, a pottage of cheese and meal, sweetened with honey and laced with wine, but also laced with one of her potions, and she turned them all into pigs with a wand after they gorged themselves on it. Only Eurylochus, suspecting treachery from the outset, escaped to warn Odysseus and the others who had stayed behind at the ships. Odysseus set out to rescue his men, but was intercepted by Hermes, who gave him the holy herb moly to protect himself from Circe's potion and, having resisted it, he told him to draw his sword and act as if he were to attack Circe. From there, Circe would ask him to bed but Hermes advised caution, for even there the goddess would be treacherous. She would take his manhood unless he had her swear by the names of the gods that she would not.
Circe ran a magical beauty salon on an island in the Sea of Monsters. She was extremely glamorous, and sometimes went by the alias of C.C. Although she treated females to a spa treatment, she turned all males who came to the island into guinea pigs. She formerly turned them into actual pigs, but found them too hard to take care of. She had captured Blackbeard and his crew mates and kept the ships in harbor. When Percy and Annabeth came, she turned Percy into a guinea pig by tricking him into drinking a magic potion. When Annabeth found out, she used Hermes' multivitamins to become immune to Circe's sorcery and free Percy from his curse and make their escape on the Queen Anne's Revenge. When trying to save Percy, she couldn't tell which guinea pig was Percy however, so she stuffed all of the multivitamins in the cage, also freeing all of the pirates that were also captured.
Annabeth and Percy reminisce about their previous encounter with Circe, with Annabeth saying to Percy that he made a "cute guinea pig" much to his chagrin. She then gives him a hint that she likes him, which Percy does not understand.Medea mentioned that Circe is her aunt, and that she had taught her the ability of charmspeaking.
It was revealed that Reyna and her sister, Hylla, were at C.C.'s Spa and Resort when Percy and Annabeth were there. After Annabeth gave the pirates Hermes' Multivitamins, they became immune to Circe's magic and subsequently took over her island, forcing Reyna and Hylla to flee.
Circe was described to be a very beautiful woman with long dark hair braided with threads of gold and piercing green eyes. She wore a silky black dress with shapes that seemed to move in the fabric: animal shadows, black upon black, like deer running through a forest at night.
Circe possesses the standard powers of a goddess.
- Mystiokinesis: As a Goddess of Magic, Circe has absolute control and divine authority over magic, but not quite as much as Hecate. However, she is still a formidable goddess-level sorceress.
- Transformation: Circe was infamous for her ability to transform men into animals, particularly guinea pigs (real pigs during ancient times). She achieved this through the use of a magic potion.
- Weaving: As shown in The Sea of Monsters, Circe is a talented weaver - her hands were said to "weave colored thread back and forth with amazing skill". Besides this, a tapestry of hers was described to shimmer like it was three-dimensional.
- Pyrokinesis: Circe has minor pyrokinetic abilities, shown when she made a flame appear in her palms.
- Charmspeak: Circe has the ability of charmspeak, which allowed her to influence others with enhanced vocal persuasiveness. Her singing was said to "drift through the air like a lullaby", and seemed to have an alluring effect, given how Percy described her voice seemed to "lift me (him) off the steps and carry me (him) toward her". Later on, she used charmspeak to enchant Percy into drinking a potion that turned him into a guinea pig in The Sea of Monsters. Medea also claimed in The Lost Hero that Circe taught her charmspeak.
- In mythology, Circe's parents were either Helios and Perseis or Aeetes and Hecate. This differs from her parentage in the books, which is said to be Helios and Hecate. This is most likely a change made for the series.
- In The Mark of Athena, Chrysaor planned on selling Hazel and Piper to her as slaves or trainees. It is unknown, however, if Circe managed to take her island back from Blackbeard sometime after Reyna and Hylla left, or possibly she opened a new spa.
- Circe has been mentioned in every book of The Heroes of Olympus series released thus far.
- Pasiphaë and Circe share the same title: Immortal Sorceress.
- In the myths, Circe was said to have given enchanted food to Odysseus' men, causing them to transform into pigs after their consumption. Odysseus was immune to the food's magic only because he ate special herbs that were given to him by Hermes.