As a descendant of the Titan Helios, the niece of the sorceress Circe, and a priestess of the goddess Hecate, Medea was a powerful sorceress renowned for her healing skills and her proficiency in using herbs and drugs.
Medea claimed that when the original Jason was sent on a quest to find the Golden Fleece, Aphrodite made her fall deeply in love with him. Medea's 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 Golden 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 after the death of Jason's uncle Pelias, Jason left her in order to marry Princess Glauce instead. Glauce (also known as Creusa) was a daughter of Creon, king of Corinth. Medea was heartbroken by Jason's betrayal and wrought a terrible revenge. She poisoned Princess Glauce and the people of Corinth. In her anger, she even murdered her two children from her marriage to Jason. Helios, her grandfather, then sent a flying chariot driven by golden sun dragons to take her away to Athens.
Other references tell a different story. After obtaining the Golden Fleece, they went to Iolcos to renew the youth of Pelias. Aeson, Jason's father, was the rightful King of Iolcos but Pelias (his half brother and a son of Poseidon) usurped the throne. He sent Jason to find the Golden Fleece so that no one would get in his way of usurping the throne, and so that he would regain his youth. Pelias assumed that Jason would die in the mission and told Aeson about his intentions. In grief, Aeson drank poison.
Unexpectedly for Pelias, Jason succeeded in the mission, with Medea's help. When Jason and Medea returned, Pelias refused to give up the throne. Medea tricked Pelias' daughters into killing him: she told them to cut him up into pieces and boil the pieces, assuring them that this was for restoring their father's youth. Jason was unfaithful to Medea and sought to replace her with Princess Glauce as his new wife. Medea murdered Glauce and, to spite Jason, killed their children as well. Then 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 Theseus would become king instead of her son, 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 to kill him by mixing poison in his wine. Just before Theseus could drink the wine, Aegeus knocked the wine cup out of his hands. Aegeus recognized Theseus as his son and successor and became aware of Medea's deceptions. Aegeus banished Medea and she supposedly fled to Asia.
Dionysus mentions Medea as one of the people Percy should ask if he wants to know how heroes always betray women and confirm that heroes are a selfish lot.
Jason Grace, Piper McLean, and Leo Valdez come to her underground mall, M's, after following some venti, where Medea introduces herself only as the Princess of Colchis. She begins to show the demigods her stock of magic objects and potions. She shows a momentary flash of anger when she hears the name of Jason, same as that of the hero who betrayed her. Soon, Piper realizes that Medea is up to no good. When Jason and Leo seem 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.
Medea is revealed to have captured Coach Hedge and the venti (caged in the bottom floor of the mall). The demigods ask for the price to retrieve the captives. Medea says the price would be quite high since the trade is unfair, and that the person buying the product is named Jason. She continues to charmspeak them to the point where they are barely listening to Piper. Medea tells them to chop each other into pieces so she could bring them back to life even stronger (the same way she killed Pelias). Leo and Jason pull out their weapons.
Piper gets Medea to admit that she can see the future. Medea reveals that she divined 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, Jason and Leo come to their senses. Medea immediately releases her two sun dragons on the two demigods. She tries to run away and Piper chases her. Piper fatally wounds Medea by throwing poisonous chemicals on her. Meanwhile, Leo summons Festus, who helps Leo and Jason to defeat the sun dragons and pick up the cages containing Coach Hedge and the storm spirits.
Just before the demigods escape, Medea cries out that she doesn't want to be abandoned again as she was by Jason. She almost manages to gain Piper's sympathy by offering to cure Jason of his amnesia. The demigods choose to leave Medea, however, when they realize that she is only trying to buy more time to destroy them. She is an agent of Gaea, and the one who Hera warned them about. As they fly away with Coach Hedge and the storm spirits , they look back to make sure the she isn't chasing them.
Later in the book, Aphrodite appears to Piper in her dream where she is shopping in Medea's mall. Aphrodite warns Piper that Medea will return later on, along with others.
It was unknown as to what her initial personality was. After the original Jason betrayed her, Medea became a vengeful psychotic, killing her own children and putting the blame on him. She even grew to hate the name "Jason" itself, as demonstrated by her encounter with Jason Grace. She also displays the mentality that she is never at fault, and that others are always to blame.
In Percy Jackson's Greek Heroes, Medea is described as being beautiful in a mysterious yet dangerous way, with shadow-dark hair that tumbled over her shoulders, eyes that flickered with knowledge of dark things, and a remorseless detached face that flushed like a girl's when she looked at Jason. She wore a black silk dress, and a golden necklace on which gleamed the symbol of Hecate - two crossed torches.
In The Lost Hero, Medea is described to look like a retired fashion model, with long dark hair swept over one shoulder, talon-like fingers with long red-painted nails, and a face that was gorgeous in a surreal super-model way. She wore an elegant black dress with diamond jewelry, and her voice was rich and exotic, with a pleasing accent.
After rising from the Underworld, she seemed to have a faint glow around her When she got angry, her face would literally glow to the extent where one could see her skull beneath her skin.
As a powerful sorceress who was descended from Helios, the Titan of the Sun, Medea possessed the abilities of:
- Mystiokinesis: Medea had the ability to control and cast magic, which she learned from her aunt, Circe. Examples of other powers she derived from her magic are:
- Amokinesis: As shown in Percy Jackson's Greek Heroes, Medea had the ability to control the emotion of love and desire - she once made Selene, the Titaness of the Moon, fall in love with a mortal.
- Magical Manufacturing: As shown also in Percy Jackson's Greek Heroes, Medea had the ability to create objects that possess mystical properties - she concocted a special ointment that granted Jason superhuman strength as well as immunity to heat and flame, and later used a magical dust to deepen the enchanted sleep that she induced upon the guardian dragon of the Golden Fleece.
- Potion Making: Medea is highly skilled in making potions. In The Lost Hero, it was shown that she was also able to make magical potions that range from healing any disease to manipulating memories.
- Chlorokinesis (possibly): As shown again in Percy Jackson's Greek Heroes, it was possible that Medea had the ability to control and manipulate plants - when the enchanted trees of the Grove of the Golden Fleece became too aggressive in their "attacks" towards Jason, Medea caused them to stop by muttering a spell.
- Charmspeak: As shown in Percy Jackson's Greek Heroes and The Lost Hero, Medea had been trained by Circe in the ability of charmspeaking, and was therefore a skillful charmspeaker despite not being a child of Aphrodite. She used this ability to sing a song of enchantment that lulled the guardian dragon of the Golden Fleece to sleep, and later on used it to put Jason and Leo under her influence, to the extent where it was only Piper's timely interference that prevented them from fighting each other to the death. Her charmspeak was so powerful that even Piper, who was herself a skillful charmspeaker, found it difficult to resist.
- Prophecy: As shown in The Lost Hero, Medea had the ability to see into the future, which she used to aid Gaea.
- Teleportation: As shown also in The Lost Hero, Medea had the ability to instantaneously transport herself from one place to another without having to physically travel through space, which manifested itself in the form of smoke.
- Medea is a legacy of Helios.
- Medea was known for potions, and was granted the ability of charmspeaking by her aunt, Circe.
- As revealed in Percy Jackson's Greek Heroes, by Hera's request, Aphrodite and her son, Eros, enchanted Medea to fall in love with Jason.
- As revealed by Piper in The Lost Hero, it was Medea who killed the children that she had with Jason, not the people of Corinth.
- Medea still kept the sun dragons that her grandfather, Helios, had given to her when she escaped from Corinth.
- Medea was mentioned three times in the Percy Jackson and the Olympians series: by Circe and Annabeth in The Sea of Monsters, and by Dionysus in The Titan's Curse, before her appearance in The Lost Hero.
- Medea used a diamond instead of a drachma for an Iris message in The Lost Hero. It is unknown how she did this.
- During Hercules' last task, he joined the Argonauts and later, left them to continue with his labours. In the Underworld, he met Theseus, long after he had slain the Minotaur. But Jason met Medea a few months after Hercules' departure, and Theseus met Medea before he slew the Minotaur, after which he went to the Underworld. This is currently an unsolved error.