FTP, identify this hero from Greek mythology and friend of Theseus.
He was the son of Dia and Ixion, and he met his best friend by stealing his cattle from Marathon.  His wedding to Hippodamia provided the setting for the battle between the Centaurs and the Lapiths, which he participated in.  Following Hippodamia's death, he made a pact with his best friend to marry a daughter of Zeus and chose Persephone as his bride.  Upon entering the underworld, he and his friend were tricked into the Chair of Oblivion, where they remained until later rescued by Herakles.  FTP, identify this hero from Greek mythology and friend of Theseus.
He was the son of Dia and Ixion, and he met his best friend by stealing his cattle from Marathon.  
Pirithous