Medea

is Mars's wife and one of his High Martians. Medea is also referred to as the by Mars.

Personality
Medea is presented as a very quiet woman who appears entirely loyal to her lord Mars from her first appearance, merely talking when needed. However this is a facade and Medea is in fact a power-hungry, coldhearted and manipulative individual. She would use and betray anybody for her plans to succeed and has done this even to those who have put their utmost trust on her without any remorse whatsoever.

Background
In the battle between Athena and Mars, Medea summons a meteorite composed of darkness that causes every Saint to get elemental powers. She and her brother Amor intended to use the war god to fuse his and Koga's Darkness Cosmo to awaken their true master Abzu.

Past
Medea along with her brother Amor were born with a great Dark Cosmo, and so were discriminated against. At the time, Medea always protected and cared for her brother. One night people tried to kill them both, but she awoke and killed them all with her cosmo. Amor found this to be beautiful and wanted to see more things like that.

First Holy War
Medea is seen in the Darkness Ruins, calling for help from a being of darkness, which sends a meteor with darkness on the battlefield, changing with the help of Athena of the cosmo, the galaxy and Cloth.

Representative of Mars
Medea eventually became Mars' wife and the imperial sorceress of his army, as well as the mother of his second child Eden. Stepmother Sonia, she's the one who ordered the girl to dispose of Southern Cross Kazuma before the rise of the Martians, in addition to several other Martian strikes against the Saints of Athena during the period when Mars was sealed. She also influenced the decision to keep Aria isolated from the outside world.

Babel Tower
When conflicts with the Bronze Saints begin, Medea prefered to simply observe events rather than play an active role. This behavior is seen when in a conversation between Mars and Leo Mycenae, she gives no substantial input but merely to sketch a slight smile. It is also present during Mars' announcement of his orders for the co-opted Saints to hunt the renegade Bronze Saints and bring Aria, alleged reincarnation of Athena back to the Babel Tower. Medea is later seen looking into her crystal ball, noting that the Cosmo of Sagittarius Seiya had faded, and continues to watch Kido Saori, captured by her husband and stuck in a tree on the planet Mars.

New 12 Zodiac Houses Battle
When the Bronze Saints begin to invade the Twelve Houses created by Mars, Medea remains at his side and follows the conflict through a set of balls. On witnessing the true strength of the Bronze Saints, the witch converses with Leo Mycenae and asks him to stop them, explaining about the darkness of the cosmo within Koga  that could be awakened in a future battle. In her room, Medea witnesses some of the Saints' triumphs, among them the victory over Mycenae via Eden, who realized they were following the wrong path and betrayed Mars. Enraged, she summons Horlogium Tokisada, one of the minions of her ally Capricorn Ionia, giving him the Aquarius Cloth, but not before informing that the new patent would completely control the wearer. Tokisada stops Koga and his friends a few meters short of the Libra House; however, to her chargin, he is defeated in a humiliating manner by Libra Genbu, who proves to be a God Saint loyal to Athena. Medea rages again and, with the strength of her cosmos, tries to destroy the twelve houses prematurely. However Genbu prevents the destruction with his cosmo.

After the events of Libra House, Medea summons her stepdaughter, Sonia, and tells the story of the constellation Scorpio, telling her that her duty is to punish Eden so that he may repent of his rebellion. With this, Medea delivers Sonia the Scorpio Cloth, telling her she would earn her love and respect if she succeed in her mission. However, this was in fact a lie, as Medea never felt Sonia was  like a daughter to her at all; furthermore, she knew all along that the Scorpio cloth was incompatible with Sonia's Cosmo, and that using the constellation's maximum power would result in Sonia's death, as takes place with Sonia's ensuing battle with Lionet Sōma.

Disturbed to see that the Bronze Saints were close to their goal, as well as seeing her son Eden turn against the ideals of Mars, Medea is faced with the presence of Leo Mycenae in her quarters. Mycenae had finally realized that the source of all problems involving the Saints and his old master Ludwig (Mars' old name as a human) was Medea and decide once and for all eliminate her. However, he's stopped by a warrior named Amor, who reveals himself to be the Pisces Gold Saint and also the younger brother of Medea, before eliminating Leo Mycenae.

Awakening Abzu
As Earth's Cosmo is transferred to planet Mars, Medea drains the darkness Cosmo from Ludwig's body following his defeat and transfers it to Amor, before she departs to Mars. Realizing that Abzu would kill Eden, Medea teleports Eden to a safe place, where the staff of Aria was saved. Medea reveals that Eden could become the new king of the world if Abzu destroys the power of the staff, but he is reluctant and willing to face it to protect the world Aria so loved. For the first time, Medea loses patience and confronts her son, using her cosmo to immobilize him. Medea tells Eden that only the dark deserved value in this world, because it was the only thing that protected her until then. Eden refuses to listen to her and counterattacks with his hit "Orion's Devastation." To the surprise of Medea, the staff of Aria protects him from her attack. Medea shows up regretting having let her son anywhere near Aria as children, and even finds it ironic that he was protected by the "light" that she so abhorred.

Aware that Eden was ready for the final battle, Medea throws herself in front of him to protect him from Abzu's attack. The god of darkness was deeply irritated by the light emanating from the staff that held Eden. Medea's last words were: "Live and be strong, Eden." And so, her body completely disappears in darkness.

Abilities
Just like characters such as Athena or Pandora, Medea lacks physical prowess, but is still capable of incredible feats. She has more than enough power to destroy the Twelve Houses of the Zodiac if she desired by cracking them apart, and it takes the power of a Gold Saint like Genbu to prevent this from happening. She also seems to be capable of influencing Gold Clothes, as she gave the Aquarius and Scorpio Cloth, to Tokisada and Sonia respectively, even though Clothes must acknowledge their users first before they can be used, which suggests that she can exert control over them. She is also capable enough of handling the enormous amount of Mars' Darkness Cosmos with seemingly no difficulty, and even though she claimed it was too much for her, she did not seem troubled on the least. Medea also has the ability to cast illusions and was successful in tricking Koga into thinking Athena was killed so that he would give into his Darkness Cosmos completely. She can also observe everything through her Crystal Orbs.

Trivia

 * In Greek mythology, Medea was the princess of Colchis, the niece of the goddess Circe, granddaughter of the Titan Helios and a powerful sorceress. When the Greek hero Jason came to ask her father, King Aeetes, for the legendary Golden Fleece, the goddesses Hera and Aphrodite caused Medea to fall in love with Jason and offer to help him with her magic. She aided Jason in gaining the Golden Fleece and escaping the wrath of Aeetes, and, upon returning to Greece, helped orchestrate the death of Jason's malicious uncle, King Pelias, by tricking his daughters into boiling him alive. In return for her services, Jason married Medea and made a sacred vow to remain with her. However, the couple were exiled to Corinth, where Jason was convinced to break his vow and marry the princess Glaucis, daughter of King Kreon. In retaliation, Medea gave the princess a cursed robe, which set Glaucis ablaze as she put it on, killing her and everyone within reach. Furthermore, Medea murdered her two sons by Jason and escaped the city in a flying chariot. Years later, she found a new love interest in King Aegeus of Athens and gave birth to his son, Medus, but when Aegeus' long lost son, Theseus arrived, Medea plotted to kill him to ensure her son would remain in power.  Despite her attempt, Aegeus recognized Theseus as his son by the sword he was carrying and, according to Herodotus, Medea fled with her son to the Iranian Plateau, where they would live amongst the Aryans, who would later come to be known as the Medes, and they would lay the foundations of the Persian Empire.  Due to Jason's betrayal of Medea, upon her death, the gods allowed Medea's soul to go to the Elysian Fields (a special place in the Underworld for the souls of the blessed).
 * Medea's connection to the mythic Princess Medea of Colchis is shown in her title of Imperial Sorceress (the Medea of Greek legend was a powerful witch and was of royal blood).