Svaðilfari

[1][2] Völuspá hin skamma, contained within Hyndluljóð, states that Svaðilfari fathered Sleipnir with Loki:[1] In chapter 42 of the Prose Edda book Gylfaginning, High tells a story set in the early days and after the gods had established Midgard and built Valhöll about an unnamed builder who offered to build a fortification for the gods to protect them from bergrisar and hrímþursar.

Under Loki's advice, it was agreed that if the work was completed in one winter with the help of his horse Svaðilfari, the builder would be given Freyja, the sun, and the moon.

[5][6] Because of his role in the making of the wager, the gods declared that Loki would face severe repercussions if he did not think of a way to cause the builder fail to complete his task.

That night, the builder drove out to fetch stones with Svaðilfari, and out from the woods, into the clearing, ran a beautiful mare who was, in fact, Loki in disguise.

As the two horses ran around all night, the building work could not be finished in time and realising this, the builder went into a rage (Old Norse: jötunmóð), revealing he was a bergrisi.