Geryon was a giant (not to be confused with the Gigantes) in Greek mythology, who lived on the island Erytheia of the Hesperides. He was the son of Chrysaor and Callirrhoe. He was often considered a monster with three heads and one body, while other sources describe him as having three bodies as well. He had a dog with two heads, Orthrus, which was the brother of Cerberus, guardian of the Underworld.
Geryon played a major role in the Labours of Heracles. The tenth labour of the hero was to take the cattle of Geryon and return them to Eurystheus. To reach Erytheia, Heracles had to cross the Libyan desert; at some point, he got so angry at the heat and the sun that he shot an arrow towards the sun. Helios, the Sun God, admired Heracles' courage, so he decided to offer him a golden cup with which he was able to sail across the sea and reach his destination.
As soon as he stepped foot on Erytheia, Orthrus tried to stop Heracles. A single blow with his club was enough to kill the dog. The same thing happened when Geryon's herdsman, Eurytion, tried to stop him. When Geryon heard what happened, he swiftly took his three shields, three spears and three helmets and went after Heracles. However, Heracles, having smeared the blood of the Lernaean Hydra on the tips of his arrows, shot an arrow against the giant and killed him by piercing through his skull. Thus died Geryon.