Geryon fights Heracles
Geryon was a three-headed giant, the son of Chrysaor and Callihroe, thus grandson of Medusa and Poseidon. He owned a herd of cattle. His watchdog was Orthrus.
Heracles
Heracles came to steal the cattle from Geryon as part of his 10th labour. Whilst he was travelling through the desert, Heracles, tired of the burning sun, shot an arrow at Helios. Helios, in admiration, gave him a golden cup, which he used to sail to Geryon's island home. Heracles killed Geryon and Orthrus with posionous arrows and stole the cattle.