Perseus (Greek: Περσεύς), the legendary founder of Mycenae and of the Perseid dynasty of Danaans there, was the first of the mythic heroes of Greek mythology whose exploits in defeating various archaic monsters provided the founding myths of the Twelve Olympians. Perseus was the Greek hero who killed the Gorgon Medusa, and claimed Andromeda, having rescued her from a sea monster sent by Poseidon in retribution for Queen Cassiopeia declaring herself more beautiful than the Nereids.
Perseus was the son of Zeus and Danaë, who by her very name, was the archetype of all the Danaans. She was the only child of Acrisius, King of Argos. Disappointed by his lack of luck in having a son, Acrisius consulted the oracle at Delphi, who warned him that he would one day be killed by his daughter's son. Danaë was childless and to keep her so, he imprisoned her in a bronze chamber open to the sky in the courtyard of his palace: This mytheme is also connected to Ares, Oenopion, Eurystheus, etc. Zeus came to her in the form of a shower of gold, and impregnated her. Soon after, their child was born; Perseus — "Perseus Eurymedon, for his mother gave him this name as well" (Apollonius of Rhodes, Argonautica IV).
Fearful for his future but unwilling to provoke the wrath of the gods by killing Zeus's offspring and his own daughter, Acrisius cast the two into the sea in a wooden chest. Danaë's fearful prayer made while afloat in the darkness has been expressed by the poet Simonides of Ceos. Mother and child washed ashore on the island of Seriphos, where they were taken in by the fisherman Dictys ("fishing net"), who raised the boy to manhood. The brother of Dictys was Polydectes ("he who receives/welcomes many"), the king of the island.
After some time, Polydectes fell in love with Danaë, so Perseus, who knew that Polydectes had grim intentions, constantly protected his mother from him. Polydectes desired to remove Perseus from the island so he could have Danaë, and therefore hatched a plot to send him away in disgrace. Polydectes held a large banquet where each guest was expected to bring a gift. Polydectes requested that the guests bring horses, under the pretense that he was collecting contributions for the hand of Hippodamia, "tamer of horses". The fisherman's protégé had no horse to give, so he asked Polydectes to name the gift, for he would not refuse it. Polydectes held Perseus to his rash promise, demanding the head of the only mortal Gorgon, Medusa, whose very expression turned people to stone. Ovid's anecdotal embroidery of Medusa's mortality tells that she had once been a woman, vain of her beautiful hair, who had lain with Poseidon in the Temple of Athena. In punishment for the desecration of her temple, Athena had changed Medusa's hair into hideous snakes "that she may alarm her surprised foes with terror"
Athena instructed Perseus to find the Hesperides, who were entrusted with weapons needed to defeat the Gorgon. Following Athena's guidance, Perseus sought out the Graeae, sisters of the Gorgons, to demand the whereabouts of the Hesperides, the nymphs tending Hera's orchard. The Graeae were three perpetually old women, who had to share a single eye. As the women passed the eye from one to another, Perseus snatched it from them, holding it for ransom in return for the location of the nymphs. When the sisters led him to the Hesperides, he returned what he had taken.
From the Hesperides he received a knapsack (kibisis) to safely contain Medusa's head. Zeus gave him an adamantine sword and Hades' helm of darkness to hide. Hermes lent Perseus winged sandals to fly, while Athena gave him a polished shield. Perseus then proceeded to the Gorgons' cave.
In the cave he came upon the sleeping Stheno, Euryale and Medusa. By viewing Medusa's reflection in his polished shield, he safely approached and cut off her head. From her neck sprang Pegasus ("he who sprang") and Chrysaor ("bow of gold"), the result of Poseidon and Medusa's meeting. The other two Gorgons pursued Perseus, but, wearing his helm of darkness, he escaped.
On the way back to Seriphos Island, Perseus stopped in the kingdom of Ethiopia. This mythical Ethiopia was ruled by King Cepheus and Queen Cassiopeia. Cassiopeia, having boasted herself equal in beauty to the Nereids, drew down the vengeance of Poseidon, who sent an inundation on the land and a sea serpent, Cetus, which destroyed man and beast. The oracle of Ammon announced that no relief would be found until the king exposed his daughter Andromeda to the monster, and so she was fastened to a rock on the shore. Perseus slew the monster and, setting her free, claimed her in marriage.
In the classical myth, he flew using the flying sandals. Renaissance Europe and modern imagery has generated the idea that Perseus flew mounted on Pegasus (though not in the paintings by Piero di Cosimo and Titian).
Perseus married Andromeda in spite of Phineus, to whom she had before been promised. At the wedding a quarrel took place between the rivals, and Phineus was turned to stone by the sight of Medusa's head that Perseus had kept. Andromeda ("queen of men") followed her husband to Tiryns in Argos, and became the ancestress of the family of the Perseidae who ruled at Tiryns through her son with Perseus, Perses. After her death she was placed by Athena amongst the constellations in the northern sky, near Perseus and Cassiopeia. Sophocles and Euripides (and in more modern times Pierre Corneille) made the episode of Perseus and Andromeda the subject of tragedies, and its incidents were represented in many ancient works of art.