Tyro was married to Cretheus, but was in love with Enipeus, the patron god of the river. One day, Poseidon filled with lust disguised himself as Enipeus and had intercourse with Tyro. As a result, Tyro gave birth to twin sons Neleus and Pelias. In desperation, Tyro exposed her sons on the mountain, a housekeeper found them and raised them. When the two men grew up, they found Tyro and killed their stepmother Sidero because they knew she had mistreated their mother. Sidero hid in the temple of Hera, but brave Pelias speared Sidero on Hera's pristine altars, thus Hera's extreme hatred of Pelias.
Pelias wished to gain supreme power over Thessaly. So he banished Neleus and kept his half-brother, Aeson locked in the dungeons of Ioclus. Aeson married and had children while in the dungeon. The most famous of these children is Jason. Aeson and his wife sent Jason to Centaur Chiron on Mount Pelion. While Jason was learning the arts from Chiron, Pelias was warned by the Oracle to beware a one sandled man because that man would cause his downfall.
Years later while Pelias was holding the Olympic Games in honor of Poseidon his father, Jason was in such a rush to get to Ioclus, that while helping someone cross the river, he lost one of his sandals. When Jason arrived at Ioclus he was announced as the man with one sandal, so a frightened Pelias asked Jason what would he do if he were faced with a man he knew would be his downfall. Jason said he would send the man to retrieve the Golden Fleece. So that is what Pelias did, and Jason began the voyage known as the Argonautica.
Hera planned for Jason to meet Medea and fall in love with her so that Medea could go to Ioclus and destroy Pelias, for Hera was still mad at Pelias for defiling her alter. This is the same Medea that was married to Aegeus and convinced Aegeus that Theseus was not his son.
Pelias thought that the Argo had sunk so he allowed heart broken Aeson to to kill himself by drinking poison. Pelias then, sacrificed Jason's younger brother.
When Jason returned with the fleece, Pelias still did not relinquish his throne. So, Medea devised a plan to kill Pelias. She told Pelias' daughters that she could make an old ram into a young ram. She then cut the old ram into pieces and threw them into a cauldron and boiled them. When Medea revealed the concoction to Pelias' daughters, out jumped a young ram. The daughters were convinced and that night went into Pelias' room and chopped him into tiny pieces. The daughters took the pieces to Medea for the boiling. When the mixture was ready, the only thing in the cauldron was a smelly, gushy slop and that was the end of Pelias.