Medea

Medea was the Princess of Colchis, the land that held the Golden Fleece in the time period of the original Jason.

History
When the original Jason, was sent on a quest to find the Golden Fleece, Medea fell deeply in love with him, by Aphrodite's hand according to Medea. Her father agreed to grant Jason his request, but only if he accomplished impossible and deadly tasks. With the help of Medea's magic, Jason was able to steal the Fleece from the king and escape.

Jason at first agreed to take Medea with him and marry her upon returning to Greece, which he did. But soon afterward he left her in order to marry Princess Creusa instead, following the death of King Pelias. Heartbroken, and looking for revenge, Medea wrought a terrible revenge by poisoning Princess Creusa and the people of Corinth, in anger murdered Medea's two children from her marriage to Jason. Helios, Medea's grandfather, then sent a flying chariot driven by golden sun dragons to take her away to Athens.

However from other references, it is said that after obtaining The Golden Fleece, they went to Lolcos to renew the youth of Jason's uncle, Pelias. Aeson, Jason's father, was the rightful King of Lolcos but Pelias (his half brother and a son of Poseidon) took over the throne. He sent Jason to find The Golden Fleece so no one would get in his way of usurping the throne and so that he would regain his youth. Assuming that the mission caused Jason's death, he told Aeson about it, thus causing him to drink poison, but with the help of Medea, Jason succeeded. When Jason and Medea returned, Pelias refused to give up the throne. Medea persuaded Pelias' daughters to cut him up and boil the pieces, assuring them that this was part for restoring their father's youth. When Jason was unfaithful to her and sought to replace her with Glauce, the daughter of King Creon, as his new wife, she murdered Glauce and, to spite Jason, his and her own children as well. From this situation she escaped to Athens.

At Athens, Medea was married to King Aegeus and had another son, Medus. One day, Theseus came to Athens. Medea recognized him as King Aegeus' son and worried that he would become king instead of Medus. So she sent Theseus to capture the Marathonian Bull, an emblem of Cretan power. Theseus returned victorious, and sacrificed the bull. Medea then tried poisoning him. At the last second, Aegeus recognized the sandals, shield, and sword, and knocked the poisoned wine cup from his hands. He banished Medea and she supposedly fled to Asia. She came back to life in the Heroes of Olympus series to serve Gaea.

The Titan's Curse
Dionysus mentions Medea as one of the people Percy should ask if he wants to know how heroes always betray women.

The Lost Hero
Jason, Piper, and Leo come to her mall, M's, where she introduces herself only as the Princess of Colchis. She begins to show the demigods her stock of magic objects and potions, but becomes angry when she hears Jason's name, as he is named after the hero that betrayed her. It quickly becomes evident to Piper that Medea is up to no good. When Jason and Leo seemed to want to keep shopping, Piper notices that Medea is charmspeaking them into buying whatever she wants them to. Piper attempts to snap them out of it with her own charmspeak and the stories of the horrible things Medea committed in the past.

As Medea continues to charmspeak them to the point that they are barely listening to Piper as Medea tells them to chop each other into pieces and she would bring them back to life even stronger (the same way she killed Pelias). As Leo and Jason pull out their weapons, Piper gets Medea to admit that she can see the future and knew that Leo would rise up against Gaea, so she warned Gaea from the Underworld. This event set in motion the awakening of Gaea and the death of Leo's mother. As a reward, Medea was set free of the Underworld and allowed to return to the land of the living, as long as her mall remained underground so Gaea could keep watch on anyone that entered.

Eventually, the two come to their senses, and they blow up the mall after Festus appears, who helps Leo and Jason to defeat the two sun dragons which attacked them by order of Medea. Medea shouts that she will not be abandoned again as she was by Jason and almost manages to gain Piper's sympathy. They choose to leave her, however, when they realize that Medea was only trying to buy more time to destroy them. She is an agent of Gaea, and the one who Hera had warned them about. As they fly away with Coach Hedge and the storm spirits (caged in the bottom floor of Medea's mall), they look back to make sure the she wasn't chasing them. Later, Aphrodite said that Medea will return later on, along with others.

Appearance
She is described as a beautiful, thin woman with long red painted-nails, long dark hair and a gorgeous face. She looks like a model and wears an elegant black dress with diamonds jewelry. After rising from the Underworld, she seems to have a faint glow around her and when she gets angry, her skin becomes slightly transparent causing her skull to become somewhat visible.

Trivia

 * Medea used a diamond instead of a drachma for an Iris message in The Lost Hero. It is unknown how she did this.
 * She was known for potions.
 * She was given the ability to charmspeak by Circe as mentioned in The Lost Hero.
 * She still keeps the sun dragons her grandfather Helios had given to her when she escaped from Corinth.
 * Medea is mentioned twice in the Percy Jackson series before her appearance in The Lost Hero, by Circe in The Sea of Monsters and by Dionysus in The Titan's Curse. Circe uses her as an example for strong sorceresses and Dionysus puts her as an example for heroes using people and then tossing them away.
 * Some myths says that Medea killed her children that she had with Jason and not the people of Corinth killed her children (Piper mentions it in The Lost Hero, saying that this is the true version).
 * Some myths say that Aphrodite and her son Eros (a.k.a Cupid) enchanted Medea to fall in love with Jason.
 * She is a legacy of Helios.