Introduction
Uchchaihshravas, "of neighing aloud", is a divine horse, described as brilliantly white, that emerged from the churning of the ocean of milk, and is closely associated with Indra.
The churning of the ocean
Among the various beings and objects produced by the Samudra Manthan, Uchchaihshravas emerged as one of the most prized, and, according to most accounts, went to Indra, though the Mahabharata's version of the story instead has him arise separately and become the object of dispute between Kadru and Vinata.
The wager of Kadru and Vinata
In the Mahabharata's Adi Parva, the sisters Kadru and Vinata argue over whether Uchchaihshravas's tail is white or black, with the loser to become the winner's servant. Kadru secretly instructs her serpent sons to cling to the tail and darken it with their bodies, winning the wager unfairly and enslaving Vinata, a servitude only ended years later when Vinata's son Garuda obtains the nectar of immortality to free her.
Later use
In some Puranic king-lists, Uchchaihshravas is also associated with later mythic and legendary kings and heroes as an ideal of the perfect horse.