Arion

Immortal horse. Arion was the offspring of Poseidon and Demeter. Poseidon lusted and chased after his sister Demeter, not long after Persephone's abduction. Demeter tried to hide from her brother by changing herself into a mare, hiding among the other horses in Arcadia. Nevertheless, Poseidon found her and transformed himself into a stallion, mounting her. Demeter gave birth to a girl named Desponia and a colt known as Arion.

Arion was owned by Oncius in Arcadia. Arion was fabulously swifter than any other horses. Heracles won Arion from Oncius. However, Heracles gave up Arion to Adrastus, the king of Argos.

In the war of the Seven Against Thebes, when the Thebans defeated the Argives, Arion saved Adrastus' life by carrying the king from the battlefield, bringing him safely to Athens.