Founding myths usually involve the slaying of some kind of archaic monster, perhaps the idol of a previous religion or some symbol. In this case, it was Medusa, who was brought to Greece from Libya, where she was worshipped by the Amazons as Metis, a serpent goddess. Cetus was a constellation first seen years before the Greeks by the Mesopotamians, who labelled it as some sort of huge sea-creature in the sky that represented the all-encompassing female principle, called Tiamat. Along the way, the Greeks must have adopted part of their version of the nightly heavens and conveniently used Cetus as the monster that terrorised Ethiopia.
The murder of Medusa and killing of Cetus by Perseus, the first hero and founder of Mycenae, obviously reflects how the Greeks asserted their superiority and authority over others and to demote the role of females and female goddesses. As the Greeks believe the Amazons and Mesopotamians were nothing but brutish savages on account of their matriarchal society, it was easy to turn their deities into nothing more than some sort of monster to be slain, an easy way to incorporate and destroy other societies and religions in order to glorify their own patriarchal ones.
This is emphasised as Perseus saves Andromeda, a maiden that must be sacrificed to appease a god, as the result of her mother’s hubris in boasting that she (mother or daughter) is more beautiful than the Nereids. In this story, women are portrayed as being helpless, vain and monstrous, or simply the instigator of trouble. Danae as the woman for whose sake Perseus goes on the dangerous quest, Medusa as the ‘monster’ he must kill, Andromeda as the woman he saves, Cassiope as the reason he had to save Andromeda in the first place, and perhaps even the Nereids, for complaining to Poseidon. All in