(Medusa)

Medusa once served under Athena as a priestess in one of her temples. This all changed one evening when Poseidon assaulted the unsuspecting Gorgon. As a consequence of his actions, Medusa was stripped of her title and afflicted with a curse that turned her head of hair to snakes. Desperate to redeem herself, Medusa continued to worship her Goddess despite her banishment. Unable to comprehend the full extent of her powers at first, Medusa was horrified to learn that she could turn others into stone. A trait that was secretively shared with her sisters, who were also punished, as Hera wanted to ensure that none of the Gorgons would ever find happiness. After freezing several civilians, Perseus would be summoned to behead her and after a long battle, was successful in bringing the gorgon to her knees.

Following the decapitation of Medusa's head, Athena later learns of Poseidon's wrongdoing and shows remorse for transforming her into a monster. To atone for ruining the gorgon's life, Athena would adorn her shield in the face of Medusa, who remained loyal. While Poseidon returned to the seas after a stern lecture from Athena. 

(Medusa has been covered in several books of mine. Each with differing timelines. Below is a collection of various interpretations of Medusa in my books.):

In Rise of the Olympians: Medusa and Arachne are tortured allies who were turned into monsters by Athena. The two want revenge against the Gods and with their newfound powers, stage an ambush atop Mt. Olympus, slaughtering all but Athena and Zeus, the former pleading for their forgiveness, whilst Zeus threatens to strike them down with his bolts. After a harrowing battle against Arachne, who's taken out by a bolt to the chest. Medusa is eventually overwhelmed by the arrival of Perseus and accepts her fate, lowering her head as he chops her head off. 

In The Gruffian Chronicles: Medusa was the kindest sister to Barratoqa, defending her from Stheno and Euryale's harsh words. Following her death, Medusa would continue to loom in Barratoqa's mind long after the days of Ancient Greece ended. Upon awakening, Barratoqa would speak of her sisters often, revealing to Embroyant that she and Medusa shared a close bond. Medusa would later appear to Barratoqa as a ghost, offering her sister passage into the Underworld, as the two disappeared into the darkness.