Hrimthurs

Hrimthurs was the giant who built the walls around Asgard and owner of the intelligent and magical stallion called Svadilfari. Hrimthurs claimed he could build the wall within six months. Had Hrimthurs won, the giant would receive Freyja as his bride, as well as the sun and moon. Thor killed Hrimthurs when he lost his wagers against the gods.

See building of Asgard, in Norse Creation, for full story.