Perseus is the son of Zeus, king of the gods, and one of his mistresses, princess Danae of Argos.
Acrisius, king of Argos, had only one child, a daughter. When consulting an oracle hoping for a future son by his queen, he was told it would be not his son, but his grandson who will inherit the kingdom- after killing him. Acrisius returned home troubled and made plans to keep his daughter a virgin by locking her up in a bronze tower safe-guarded by savage dogs. Unfortunately for Acrisius, Zeus saw Danae and visited her in the form of golden rain and impregnated her.
When Acrisius learnt of Danae having a baby boy, he locked her in a wooden chest with her newborn son Perseus, and threw them to sea. Under Zeus' watchful eye, the chest arrived safely on the shores of Seriphos, where the chest was drawn and opened by a fisherman, Diktys. The fisherman kindly sheltered mother and son, who took care of them well along with his wife. Perseus grew strong and handsome, learning how to use the sword and ride the horse.
Seriphos was ruled by Diktys' cruel brother, king Polydektes, who took a liking in Danae and made efforts to have her, but Perseus kept him from doing so. Thus, he planned a false pre-wedding dinner in which his friends were invited, and Perseus too was was asked to attend. It was tradition for such a feast for guests to give the bridegroom a horse, but obviously Perseus, having lived a simple way of life, had none to give. Thus Polydektes asked him for a compensating gift, the head of Medusa the Gorgon.
Perseus was well aware of the danger he was put in. Medusa was a female monster whose hair was a mass of venemous serpents and eyes so frightful they turned any creature who looked at them to stone. Luckily, the gods Athene and Hermes, Perseus' half-sister and half-brother, were aware of his situation. Athene, being the cause of Medusa's transformation from a beautiful maiden to the present horrible monster, was quite willing in helping Perseus out in his quest. She offered Perseus her shield of shining gold- this was to act as a mirror so as to look at Medusa's harmless reflection rather than directly onto her. Hermes offered a pair of his winged sandals for flight. Yet this was not enough- Perseus was told to visit three water nymphs who were to give him three more magic objects. One gave him a very sharp sword, another gave him a bag of goatskin, and the third gave him Hades' helmet of invisibility.
Perseus' last stage was to visit the Graeae. They were the sisters of the Gorgons, old from birth, who shared a single eye and tooth between themselves. Only they knew where the Gorgons lived. Perseus managed to steal away the eye and demanded they reveal Medusa's whereabouts. In despair they gave him directions, and Perseus flew to the ends of the earth. Perseus arrived and saw how the land was laid to waste. Creatures and human beings stood frozen as stone statues all over, and amidst them lay sleeping the three monstrous Gorgons. With Athene's help, Perseus made out which of the Gorgons was Medusa, and swiftly he delivered a single stroke and decapitated her, and from the blood the winged horse Pegasus and his brother the giant Chrysaor were born. He thrust the head in the bag and fled from the screeches of the other two sisters.
On his way Perseus arrived at the garden of the Hesperides. There stood the titan Atlas, who feared Perseus thinking he was the foretold son of Zeus who would steal the golden apples of Hera. In anger for Atlas' inhospitality, Perseus turned the former into stone with Medusa's head. The second stop was at Ethiopia, where Perseus chanced to see a maiden chained naked to a rock by the sea. He was informed that she was the princess named Andromeda, whose mother the queen Cassiopeia vilely compared her beauty with that of the Nereids. The latter complained to Poseidon, god of the sea, who in anger sent the monster Ketos to ravage the land. Only the sacrifice of the virgin princess would appease the sea monster, and thus Andromeda was chained ready to be devoured. On Ketos arrival, Perseus showed it Medusa's head and turned it into stone. Cepheus, Andromedas father, held a great feast in honour of Perseus wedding with Andromeda, the condition which he set for saving the princess. Alas Cepheus brother, Phineus, arrived at the palace with a small army to fight off Perseus since Andromeda was betrothed to him before. Perseus turned him and his men to stone with Medusas head.
Perseus later returned to Seriphos with his new wife, and learnt how Danae was in Athenes temple as a fugitive from Polydektes constant threats for not marrying him. He went to the palace where he turned Polydektes and his friends to stone. Athene and Hermes then returned for the magic gifts, and as thanks he offered Medusas head to Athene, who placed it on her shield to ward off enemies. He then placed Diktys as king instead. Perseus then returned to Argos, but first stopping at Larissa to compete in funerary games. Coincidentally, Acrisius also was in Larissa after fleeing from Argos when hearing of the return of Danae and her son. Perseus competed in discus-throwing, and when doing so a gust of wind blew the stone discus off course and hit Acrisius hard in the face, killing him instantly. So, the prophecy was fulfilled and Perseus inherited the kingdom, but preferred to switch with his cousin for the kingdom of Mycenae.