Hrungnir

Hrungnir is the stone-headed giant whom Thor kills in a duel, and the strongest of all the giants according to Snorri Sturluson. A piece of his whetstone is still lodged in Thor's head, and only Thor's infant son Magni can lift the giant's leg off him.

Snorri tells the story in Skaldskaparmal, in his Prose Edda. Odin rides Sleipnir into Jotunheim and wagers his head that no horse there can match it. Hrungnir, sure that his horse Gullfaxi has a longer stride, gallops after him in a fury, but Odin stays ahead, and the giant is through the gates of Asgard before he notices. Drinking from Thor's bowls, he boasts that he will carry Valhalla off to Jotunheim, sink Asgard and kill every god except Freya and Sif, whom he will take home; Freya alone dares to pour for him. When the gods call Thor, the unarmed giant challenges him to a duel at Griotunagardar, and Thor accepts, because no one has ever challenged him before.

The giants make a clay man nine leagues tall, Mokkurkalfi, with a mare's heart, who wets himself at the sight of Thor. Hrungnir's own heart is hard stone with three points, like the carved sign later called Hrungnir's heart, and his shield is stone too. Tricked by Thor's servant Thjalfi, he stands on his shield. Thor hurls Mjolnir and Hrungnir his whetstone; they collide in the air and the whetstone breaks: one half falls to earth and becomes all the world's whetstone rock, the other lodges in Thor's head. The hammer smashes the giant's skull, and he falls with his leg across Thor's neck. The sorceress Groa almost charms the stone out but forgets her spells, which is why, Snorri says, no one should throw a whetstone across a floor.

Snorri cites Haustlong, composed around 900 by the skald Thjodolf of Hvinir, which describes the duel as painted on a shield. In Harbardsljod Thor boasts of felling the giant whose head was stone, and Lokasenna calls his hammer “Hrungnir's slayer”. Grottasongr, however, says Hrungnir and his father were strong, but Thiazi stronger still.