Hercules was required to obtain the cattle of Geryon for his tenth labor, according to the account I read. Obtain is a rather bland word for steal, since Geryon wouldn’t have given them to Hercules. Geryon lived on the island of Erytheia, on the far side of the Libyan desert. By different accounts he had: three heads and one body; or three bodies; or six hands and six feet and wings; or three bodies joined to one pair of legs. All agree he was a giant, the grandson of Medusa and a badass. ‘Nuff said.
While Hercules sweated across the Libyan desert he shot an arrow at Helios, the Sun. Helios admired his courage and gave him a golden cup, which Hercules used to sail back and forth across the sea to the island.
When Hercules reached the island, Orthrus, a two-headed guard dog and brother to Cerberus, attacked him. Hercules killed the dog with his club. Then he killed the herdsman in the same manner.
Geryon arrived, carrying three shields, three spears, and wearing three helmets, chasing Hercules to the River Anthemus. At that point, Hercules shot Geryon in the forehead with an arrow dipped in the Lernaean Hydra’s venomous blood and killed the giant.
He herded the magnificent red cattle back toward home. The Romans added to the story by saying Cacus stole some of the cattle while Hercules slept but he later retrieved them from a cave…or the marketplace. Lots of versions here.
Meanwhile, Hera sent a gadfly to bite the cattle and annoy Hercules. The cattle scattered and it took a year to retrieve them all. Then Hera sent a flood into the river so they couldn’t cross and Hercules had to build a dam out of stones to lower the water.
When Hercules finally made it back home again, he presented the cattle to Eurystheus. The king then sacrificed them all to Hera.