Svadilfari

In Norse mythology, Svadilfari was a magical horse, owned by Hrimthurs. Disguising himself as a mare, Loki lured Svadilfari away from his master in order to delay him, hoping to avoid paying him for his work. (He succeeded in this.)

The result of Loki's congress with Svadilfari was the eight-legged horse Sleipnir.