Medusa Gorgon

Medusa Gorgon is the first main villain of Soul Eater and the mother of Crona, who is also the crown jewel in her master plan: the destruction the world order to get the planet back on track. She is the middle child of the three Gorgon Sisters. Lacking empathy for others, with a twisted sense of love, Medusa views everyone as a potential specimen to experiment on or as a tool to suit her purpose.

History
Eight centuries prior, after Arachne actions in creating the Magic Weapons marked her for death, Medusa severed all ties with her older sister and left her to die by Death's hand. Eventually, formulating a scheme to revive the Kishin Asura, Arachne injected her child Crona with the melted remains of Ragnarok mixed with Black Blood and proceed to make her child's life miserable. This act is intended for Crona to be at the ideal level of madness compatible with Asura's. Soon after, with blessing of the Grand Witch, Medusa infiltrated the DWMA as the school nurse in order to get close to the Kishin.

First Confrontations
Eventually, after years of turning the child into a sociopath, Medusa takes the Crona to Italy to devour souls before Maka Albern detected the child's actions at the Santa Maria Novella Basilica after Medusa casts a spell to remove her child's inhibitions. Though watching the events of Crona overpowering Maka unfold from her broom miles above the ground, Medusa is eventually forced to intervene when Crona's resonance with Ragnarok was disabled by Franken Stein and Spirit and uses her Vector Arrows to hold the Meister and Weapon duo long enough to grab the heavily injured Crona and departs. However, the fact that Maka's partner Soul ended up with some of Crona's blood mixed into his system presents interest to Medusa as she plotted to free Prisoner #13 to test the Black Blood's effect on Soul and how it would effect Maka. But when confronted by Eruka Frog over her actions endangering their kind, Medusa forced the witch into her service and has her release Free in her stead.

Having also drafted the five remaining Mizune sisters, after killing their oldest in secret for aiding Eruka, Medusa begins setting up her scheme to release Asura from his prison during a DWMA event. But as Stein has begun to caught on to her true nature and intent, Medusa quickly has Eruka destroy her house to remove any evidence of her being a witch while retrieving the vial of Black Blood prepared for Asura. The next day, Medusa sets her plan into motion by first trapping Death and all the academy students in one room. From there, with herself and Crona halting would be interlopers, Medusa has Eruka and Free use the Black Blood vial to free Asura from his prison. Finding herself facing Stien, admiring the Meister for his creativity and attempted to draft him, Medusa had the upper hand at first until she accidentally dropped her defense as she sensed the Kishin's revival. Though Stein uses Spirit to land the deathblow even after she declared her love for him, Medusa survived by using Asura's residual madness to transfer her soul into one of her snake familiars. Eventually, Medusa's soul acquires the body of a young girl by the name of Rachel Boyd.

Deceitful Manipulation
Eventually, with her new vessel, Medusa arrives to Baba Yaga's Castle where she confronts Arachne after eight centuries. The meeting almost ended in bloodshed were it not for Eruka, who infiltrated Arachnopobia under Medusa's orders. Soon after, Medusa reveals herself to Crona and convinces the child to serve as her spy in the DWMA. Once Eruka and Mizune obtain the legendary artifact "BREW", after Crona's mysterious disappearance from the institute, Medusa offers a ceasefire with the DWMA to deal with a mutual enemy: Arachnopobia. Teamed with Maka and Soul, who believed Crona is held captive by her older sister, Medusa takes them to Baba Yaga Castle's throne room where the three learn that Arachne had discarded her body and became a spiritual being of pure madness.

Incapacitated, Medusa is forced to watch her sister's demise by Maka while noticing the Meister's level of power. Once Arachne's soul is eaten by Soul, Medusa discards Rachel and transfers herself into Arachne's souless body. In her new body, Medusa gloats that she had Crona the entire time and used the DWMA to obtain an ideal body. Before Medusa could kill Maka, recognizing the girl as too great a threat to leave alive, she finds herself confronted by the Death Scythe Tezca Tlipoca and partner Enrique. Due to residual aspects of Arachne attempting to regain control, Medusa takes Tezca's offer and flees as she begins preparing Crona for the destiny she envisioned for her child: becoming one with Asura and ushering in a new order of chaos.

The Witch's Legacy
Using the Black Blood, Medusa created the Black Clown to test its abilities compared to the ones Asura produces. Though it appeared to fall against Kirikou, Medusa is delighted to see that her creation survived as she later has the Black Clown augment Crona's powers during the child's fight with Black Star. At that time, Medusa finds herself facing the renegade Death Scythe Justin Law as he absorbed a Clown to execute her for her hubris. Using her personal Purple Clown to enhance her familiars, having Crona taken to safety, Medusa engages Justin in an epic battle until Tezca's arrival allows to her leave.

Soon after, Medusa sends Crona to Ukraine to cause havoc and kill Tsar Pushka and his Meister Feodor as a experiment to test the improved Black Blood against the Anti-Demon Wavelength. Once Crona returns, Medusa acts more like a mother to her child's confusion. Eventually, with her child realizing the inablity to deal with her love or anything else, Medusa finds herself being vivisected by Ragnarok under the command of a frighten and utterly furious Crona. Once Crona finished venting, seconds away from death, Medusa reveals that she intentionally provoked Crona so the child would severe ties with everything and everyone to carry out the destiny she created. With her aspirations fulfilled as Crona delivers the final blow, Medusa calmly says her mind-burning final words: "I, love you Crona".

Anime
In the anime adaptation, Medusa's story is the same up to the events of Baba Yaga's Castle where she tricks Crona into helping her manipulate Stein by intensifying his madness using by implanting a magic snake inside of an unsuspecting Marie Mjolnir. Facing Maka, Marie, and a repentant Crona, Medusa is defeated by Maka with Genie Hunter, returning Rachel to normal while Medusa is driven out and disintegrates due to the evil-destroying powers of the Genie Hunter attack. In her final words, she tells Maka that her Genie Hunter might not be strong enough to defeat Asura.

This presumably kills her; Although the snake whose body she transferred to after her first defeat is shown in the credits of the final episode, there is nothing to suggest that Medusa's soul was actually inside the snake this time, as Medusa said during her reunion with Arachne that she only survived this soul transfer because of the waves of madness from Asura awakening and likely wouldn't survive it again.

Trivia

 * Medusa's Japanese voice actress Houko Kuwashima also voiced Lilithmon (Digimon Fusion) and Cirucci Sanderwicci (Bleach).
 * Medusa's English voice actress Luci Christian also voiced Wrath (Fullmetal Alchemist).