The tale of Hrungnir is documented in the second part of the Prose Edda, Skáldskaparmál.
Hrungnir engaged in a wager with Odin in which Odin stakes his head on his horse, Sleipnir, being faster than Hrungnir's steed Gullfaxi. During the race, which Sleipnir wins, Hrungnir enters Valhalla, and there becomes drunk and abusive. After they grow weary of him, the Gods call on Thor to battle Hrungnir.
Hrungnir hurles a flint-stone towards Thor, who in turn hurles Mjölnir, shattering both the whetstone weapon and Hrungnir's skull. After his death, the Jötunn's steed Gullfaxi was given to Thor's son Magni as a gift for releasing his father from Hrungnir's corpse.
Hrungnir was born with neither head nor heart, so his people had to complete his body with stone, thus he grew into a complete simpleton.
One day he was wandering the realm of Midgard when Odin crossed paths with him. The King of the Aesir was so amused by the stone giant's gullible nature that he invited him to his hall in Asgard to amuse his court.
After having his fill of mead, a drunken Hrungnir became rowdy and begun to threaten the Aesir, which the Aesir simply took as a joke. Then Thor arrived, took one look at Hrungnir, and decided that he was not amused. Thor then struck the giant in the head with Mjolnir so hard that chunks of Hrungnir became buried in Thor's own skull.
The thunder god was so startled by the faceful of rock, he was unprepared as Hrungnir's gigantic corpse fell right on top of him, much to the amusement of the whole court of Asgard. No one in the court was strong enough to free the thunder god and even Thor himself was unable to remove it, having gotten too drunk to exert enough strength to do, but then little Magni and Modi, no taller than shrubs at the time, entered the hall and effortlessly flipped over the stone giant, freeing their father. Despite both brothers performing the deed together, only Magni received any of the praise for the accomplishment because he simply the blonder of the duo, which left Modi bitterly jealous due to having been overshadowed by his older brother. Unknown to everyone in the room however, Odin’s advisor, Mimir, was the only one who witnessed both brothers freeing Thor.
Mimir later used his story to teach Atreus that truth is seldom as pretty as myth and legend.
Powers and Abilities
Thanks to having parts of his body made of stone, Hrungnir was an incredibly strong giant. He most likely enjoyed to fight, since he gained the nickname of Hrungnir the Brawler. After his death by Thor, Hrungir's corpse is so heavy when crushing Thor.
Kratos: "Head... you are full of stories. When will you tell one that entertains?"
Mimir: "I beg your pardon?!"
Atreus: "He just insulted you."
Mimir: "Yeah, I got that. So you want a corker, do ya? Very well, my brothers – I'll tell you the story of Hrungnir the Brawler. The real story."
Atreus: "There was a huge battle, right? His shrine had him in the middle, fighting off Aesir..."
Mimir: "A pretty story, but... no. Hrungnir, you see, was born with neither head nor heart, so the Giants had to complete him with stone. He was strong to be sure – but also a perfect simpleton. Odin met him wandering in Midgard one day – found him so amusing, so harmless, so gullible, that he invites him back to his palace in Asgard. There he gives Hrungnir his fill of mead, and goads him into all manner of boasts and antics, all for the amusement of the court. I was there – I saw the Aesir laugh as Hrungnir leapt upon his shield and swore he'd kill us all and take our womanfolk back to Jötunheim. Then Thor shows up – and does he laugh? Oh, no. Thor takes one look at the drunken stone buffoon, and brings down Mjölnir on his head so hard that he's got chunks of Hrungnir in his own skull to this day. Thor is so startled by the faceful of rock, he doesn't notice Hrungnir's body topple right onto him with a sickening crunch? And again, the roars of laughter echo through the palace halls!"
Atreus: "That's an awful story, Mimir. Nothing like the ones mother told me."
Mimir: "Let that be a lesson, m'son – truth is seldom so pretty as myth and legend."
- Hrungnir is depicted with a shield in his shrine, a shield that in Norse mythology was made from the same stone that his head and heart were made.