Dolphins in mythology
Dolphins appear in a number of Greek myths, invariably as helpers of humankind. Dolphins also seem to have been important to the Minoans, judging by artistic evidence from the ruined palace at Knossos.
A dolphin rescued the poet Arion from drowning and carried him safe to land, at Cape Taenarum, now Cape Matapan, a promontory forming the southernmost point of the Peloponnesus. There was a temple to Poseidon and a statue of Arion riding the dolphin. (Herodotus I.23; Thucydides I.128, 133; Pausanias iii.25, 4)
The Greeks reimagined the Phoenician god Melqart as Melikertês (Melicertes) and made him the son of Athamas and Ino. He drowned but was transfigured as the marine deity Palaemon, while his mother became Leucothea. (cf Ino.) At Corinth, he was so closely connected with the cult of Poseidon that the Isthmian Games, originally instituted in Poseidon's honor, came to be looked upon as the funeral games of Melicertes.
Phalanthus was another legendary character brought safely to shore (in Italy) on the back of a dolphin, according to Pausanias.
Many seals and coins show a man or boy riding a dolphin.
Dionysus was once captured by Etruscan pirates who mistook him for a wealthy prince they could ransom. After the ship set sail Dionysus invoked his divine powers, causing vines to overgrow the ship where the mast and sails had been. He turned the oars into serpents, so terrifying the sailors that they jumped overboard, but Dionysus took pity on them and transformed them into dolphins so that they would spend their lives providing help for those in need.
Dolphins were also the messengers of Poseidon, Greek god of the sea, and sometimes did errands for him as well.
In Hindu mythology the Ganges River Dolphin is associated with Ganga, the deity of the Ganges river. The dolphin is said to be among the creatures which heralded the goddess' descent from the heavens  and her mount, the Makara, is sometimes depicted as a dolphin.