Sleipnir

Sleipnir is the trusty steed of Odin and son of the Jotunn Loki.

Story
In Asgard, a huge protective rampart was almost completely destroyed in a recent war. The gods were uninterested in rebuilding the walls themselves and so left it destroyed. One day, a very skinny man riding a dark horse offered to rebuild and improve the rampart. He promised to rebuild the rampart in only 18 months in return for Freyja's hand in marriage, as well as the ownership of the sun and moon. The gods were furious with the demands, but Loki proposed to Odin to let the stranger rebuild the rampart. He suggested that if the stranger takes longer than 18 months to complete the walls, then the gods do not have to uphold their end of the bargain. Odin follows Loki's advice and told the stranger that they will agree to the demands if he could finish the walls in 6 months and receive help from no man in doing so. The stranger asked if his horse could help and Odin agreed. Strangely enough, the stranger and his horse were able to rebuild the rampart at an inhuman speed. The gods were upset that the stranger was actually a mighty jotunn, but they could do nothing as this does not violate their agreement. This horse was in fact Svadilfari.

The gods began to distrust Loki, but he assured the gods that he had a plan. Then, the reconstruction of the rampart halted suddenly as Svadilfari became missing. The gods investigated out of curiosity and discovered that Svadilfari had fallen in love with a mare. The stranger was forced to continue work on the walls alone and managed to almost finish rebuilding by 6 months. All that was left was the castle gate. The gods happily told the stranger that they could not pay him as requested due to the unfinished work. The stranger became enraged and accused the gods of tricking him. He reveals himself as a terrible frost giant, a Hrimthurs that was undergoing stone masonry training. Thor quickly killed the giant with Mjolnir by hurling it at the giant's head, which exploded into a thousand pieces. The horse Svadilfari was nowhere to be found for a long, long time.

After a while Loki, who looked tattered and worn out, brought a strange-looking pony with eight legs to Asgard. He introduced the pony as Sleipnir and presented it to Odin as a present. It turns out Loki transformed into a mare to seduce Svadilfari so it would no longer work on the rampart.

Trivia

 * Sleipnir is an eight-legged horse that is Odin's steed, the child of Loki and Svadilfari, described as the best of all horses, and is sometimes ridden to the location of Hel.