Hrungnir

Hrungnir was a giant from Griotunagardar, frontier of Giantland. He was considered to be the strongest giant in the world. His head and heart was made of stone.

Hrungnir owned a horse called Gullfaxi ("Golden Mane"), the fastest horse in the Giantland, but Odin boasted that his horse (Sleipnir) was better.

This led to Hrungri declaring he would move Valhalla to Jötunheim, and destroy Asgard and all the Aesir gods except for Freyja and Sif, whom he would take as his concubines.

Thor challenged him in a duel, but Hrungnir had come to Asgard unarmed. Hrungnir told Thor to meet him at Griotunagardar. The other giants created a giant made of clay, which they called Mokkurkalfi. They hoped to use Mokkurkalfi to frighten Thor with its enormous size; Mokkurkalfi stood nine leagues high and three leagues wide.

Armed with a large whetstone, he hurled it at Thor. Though, Thor's Mjollnir broke the whetstone in half, but one of the piece was lodged in Thor's head. Mjollnir shattered Hrungnir's stone head and fell dead on top of Thor's neck.

Thor could not push Hrungnir off him, but Magni removed Hrungnir's body off his father. Thor gave Gullfaxi to Magni.

See Giant of Clay for more details.