Perseus
Perseus (Greek: Περσεύς) is a hero in Greek mythology. He is the legendary founder of Mycenae and is most famous for killing the Gorgon Medusa. He is a demigod, the son of Zeus and the mortal princess Danaë. With his wife, the Ethiopian princess Andromeda, his children are the sons Perses, Alkaios, Sthenelos, Elektryon, and the daughter Gorgophone. Perseus is also the great-grandfather of Herakles, as well as his half-brother.
Birth
King Akrisios of Argos was told by an oracle that he would be killed by his grandchild. Because of that he put his daughter Danaë in a tower where no one was allowed to enter, so she could not have a child. But the god Zeus could enter in the form of a golden rain, and with him her child was Perseus.
Akrisios then put Danaë and her baby Perseus in a box and threw it into the sea. But Zeus tells the sea-god Poseidon to help them, and so Danaë and her son come to the island Seriphos. There they are found by Diktys, who lets them live with him.
A long time after that, the grown up Perseus takes part in some funeral games. During the games Perseus throws a discus, which accidentally hits Akrisios. Akrisios is killed by it: he was killed by his grandchild, like the oracle's prophecy said.
Perseus and Medusa
Perseus was sent to retreive Medusa's head by King Polydectes, who wanted him dead so he could marry his mother. To do this, he was advised by Athena to seek the Gray sisters, who told him how to fight Medusa when he stole their eye. Hermes lent Perseus winged sandals, Hades lent him his helm of darkness (which makes the wearer invisible), and Athena lent him a shield which he could see Medusa's reflection in, since whoever looked her in the eye would turn to stone. With all these magic items, Perseus was able to cut off Medusa's head. On the way back home, he fights a sea monster to save Andromeda, who is chained to a cliff as a sacrifice, and marries her.