It's one of the best known Hellenic myths, and the movies, series, books, comics and other mediums which feature it--or Médousa--are endless. Percy Jackson comes to mind, and Clash of the Titans, but there are many others. What's less well known is that this particular myth doesn't date back to ancient Hellas, but ancient Rome: it was written by the Roman poet Ovid, in 8 B.C., in his Metamorphosis.
"...He [Perseus] told of his long journeys, of dangers that were not imaginary ones, what seas and lands he had seen below from his high flight, and what stars he had brushed against with beating wings. He still finished speaking before they wished. Next one of the many princes asked why Medusa, alone among her sisters, had snakes twining in her hair. The guest replied ‘Since what you ask is worth the telling, hear the answer to your question. She was once most beautiful, and the jealous aspiration of many suitors. Of all her beauties none was more admired than her hair: I came across a man who recalled having seen her. They say that Neptune, lord of the seas, violated her in the temple of Minerva. Jupiter’s daughter turned away, and hid her chaste eyes behind her aegis. So that it might not go unpunished, she changed the Gorgon’s hair to foul snakes. And now, to terrify her enemies, numbing them with fear, the goddess wears the snakes, that she created, as a breastplate.’"
Yet, Médousa was a well known figure in ancient Hellas, so well known that the images of her cut off head adorned everything from armors to stoves. Her name meant 'guardian', and her head frightened off enemies as well as little children who would otherwise have burned their hands. The blood from the veins on the left side of Médousa's head was allegedly capable of killing, but Asclepius, a great healer, used the blood from the veins on the right side of the head for saving lives.
In ancient Hellas, Médousa was one of three sisters, Khthonic daímōns called Gorgons. They were named Médousa, Stheno (Σθεννω), and Euryale (Ευρυαλη), and were born to the ancient marine deities Phorkys (Φόρκυς) and Keto (Κητώ), his sister. They were part of the Phorcides (Φόρκιδες), the offspring of Phorkys. Their sisters were Echidna (Ἔχιδνα, half woman, half snake), the Graiai (Γραῖαι, 'old women', sharing one tooth and one eye), and Ladon (Λάδων, the dragon serpent who guarded the golden apples in the garden of the Hesperides). This view comes from Hesiod:
"And to Phorkys, Keto bore the Graiai, with fair faces and gray from birth, and these the gods who are immortal and men who walk on the earth call Graiai, the gray sisters, Pemphredo robed in beauty and Enyo robed in saffron, and the Gorgones who, beyond the famous stream of Okeanos, live in the utmost place toward night, by the singing Hesperides: they are Sthenno, Euryale, and Medousa, whose fate is a sad one, for she was mortal, but the other two immortal and ageless both alike. Poseidon, he of the dark hair, lay with one of these, in a soft meadow and among spring flowers. But when Perseus had cut off the head of Medousa there sprang from her blood great Khrysaor and the horse Pegasos so named from the springs (pegai) of Okeanos, where she was born."
According to Apollodorus, Médousa and her sisters came into the world with snakes on their heads, instead of hair, with yellow wings and brazen hands. Their bodies were also covered with impenetrable scales, and their very looks had the power of killing or turning to stones. Médousa was the only mortal of the three, and in nearly all versions of the myth, has her head cut off by Perseus, who gifts it to Athena. The big difference? In the Hellenic version of the myth, Médousa was never a beautiful maiden who served as a priestess to Athena and was punished for being raped.
There is a third version of the myth, inspired, it seems, by Hesiod, in which Médousa was a very beautiful maiden who lived far to the north where the sun did not reach. She begged Athena to allow her to leave and see the sun, but Athena refused. Médousa got angry and shouted at Athena that she was only disallowing her request because she was jealous at her beauty. Athena, angered, turned her into the monster she is so famous as today. There is a variation of this myth where Médousa tells the sculpture of a statue of Athena that he would have done better making a sculpture of her, because she was far more beautiful. The result is the same; Athena takes her beauty and forces her into isolation as punishment for her hubris. Apollodorus, interestingly enough, also confirms this:
"It is affirmed by some that Medousa was beheaded because of Athene, for they say the Gorgon had been willing to be compared with Athene in beauty."
Archaeologists suspect that Athena, Médousa and Poseidon found their origins in Libya. They came to Hellas through Crete at the dawn of Hellas. In the beginning of Her rein, Athena may have been a snake and fertility Goddess--a trait she shared with her Libyan counterpart, who had Her own cult--and may have either had a priestess who fit the Médousa myth or--and this is more likely--Médousa had her own cult as a snake, fertility and (menstrual) blood Goddess. Especially the latter may be linked to the myths concerning Médousa's blood.
Athena's role as a snake and fertility Goddess is still visible in the myth about the child she had with Hēphaistos; Erichthonios (Ἐριχθόνιος), who was half man, half snake. It's even posed that in the early days, Athena was married to Hēphaistos and had His child willingly. As Athena was stripped of Her roles as a fertility and snake Goddess, Médousa's myth came into being, where Athena distances Herself from sex and snakes, by punishing an epithet of herself (Athena Tritogeneia, perhaps: 'born of Trito', a lake which was supposedly located in Libya), or the Libyan snake Goddess Médousa, who may have still been attached to Her worship. By placing Médousa's head on Her breastplate or shield, Athena's mythology is continuously linked to Her Libyan heritage, but harmlessly so, to Her new image of a virginal warrior.
Few references remain to Médousa's Libyan cult. There's vague reference to Médousa being a patron of Libya as a whole, or that she was the Goddess most worshipped by the Amazons. She was linked to protection, snakes, menstrual blood, blood, fertility, and femininity in general. If this is true, it's understandable why her worship did not match the Hellenic religion: for one, she's most likely a very powerful female deity. This did not match the hierarchy of the ancient Hellens, and so, Médousa became a monster, and was dealt with accordingly. Blood was one of the fluids that caused serious miasma, and menstrual fluid wasn't even spoken of in ancient Hellas, let alone revered. Not a single Goddess would have it in their portfolio.
I don't like Ovid's version of the Médousa myth. In my view, it's an embellished version of the myth which overshoots its purpose. It also puts both Poseidon and Athena in a very bad light, and takes a lot away from Médousa. As an Hellenist, I am going to pull the Recon card and ignore the heck out of the Ovid myth. I hope that works for you as well. In all honesty, Athena can be a harsh Goddess, but most of her brutal mythology (like Arachne) applies to Minerva, Her Roman counterpart. I'm not saying these two are not linked, but I consider the Roman pantheon as a separate pantheon, with harsher deities. I'll get back to that in another post. For now, I hope this post redeems Médousa a bit, and puts her in a new light for you.