Sleipnir, known as the fastest horse of all horses and one who never tired, carried Odin the All-Father through the sky, over the seas, and across the lands. Wherever Odin went, Sleipnir was there with him. Sleipnir was easily identifiable with his eight legs. He was the offspring of Svadilfari, a massive stallion, and Loki, the Trickster and Shape Changer of Asgard. Loki shapeshifted, taking the form of a mare, to create the magical horse Sleipnir. From the moment of his birth, Odin and Sleipnir were inseparable. Source: AncientPages.com
Interesting fact:
Sleipnir cut an imposing figure with his eight legs and supernational strength.