Geirrod was a cruel and treacherous Norse giant — the jötunn who lured Thor into his hall without the thunder-god's hammer and belt, and tried to kill him by treachery, only to be destroyed by Thor in one of the giant's own deadly traps. His tale is one of cunning malice met by overwhelming divine strength, and of the helpful giantess who armed Thor against him.
The Treacherous Giant
Geirrod (Old Norse Geirröðr) was a powerful and hostile giant, the father of two fierce giant-daughters, Gjálp and Greip. His scheme against Thor began with Loki: the trickster, flying in Frigg's falcon cloak, was captured by Geirrod, who imprisoned and starved him until Loki swore to bring Thor to Geirrod's hall without his hammer Mjölnir, his belt of strength, or his iron gloves — that is, stripped of the weapons that made him invincible. Loki agreed, and lured Thor toward the giant's realm.
The Helpful Giantess
On the way, Thor stopped at the hall of a friendly giantess named Grid (the mother of Odin's son Vidar). Grid, knowing Geirrod's treacherous intent, warned Thor of the danger and lent him three precious gifts to replace his missing gear: a magical staff (Gríðarvölr), a belt of strength, and a pair of iron gloves. So armed, Thor continued on — and these borrowed gifts would save his life.
The River and the Daughters
Thor had to cross a great river that suddenly rose in a roaring flood, threatening to sweep him away. Looking up, he saw the cause: Geirrod's daughter Gjálp was standing astride the river upstream, making the waters surge with her own body. Thor hurled a great stone at her, declaring that “a river must be dammed at its source,” and stopped the flood; bracing himself on Grid's staff, he hauled himself out. At Geirrod's hall he was given a seat — which suddenly shot upward to crush him against the roof; but Thor jammed Grid's staff against the rafters and pushed back down with all his strength, crushing Geirrod's two daughters, who had been hiding beneath the seat to kill him.
The Red-Hot Iron
Then came Geirrod's final treachery. The giant seized a glowing, red-hot lump of iron from the fire with a pair of tongs and hurled it at Thor to kill him — but Thor, wearing Grid's iron gloves, caught the burning iron in mid-air. Geirrod fled and hid behind an iron pillar; Thor hurled the red-hot iron back with such force that it smashed straight through the pillar, through Geirrod, through the wall, and into the ground beyond, killing the treacherous giant. Geirrod endures as the archetype of the cunning, treacherous giant brought down by his own deadly devices — the schemer who tried to kill Thor unarmed and was instead destroyed by the very iron he hurled, his own trap turned back upon him.
He lured the thunder-god to his hall stripped of hammer and belt, and hurled red-hot iron to kill him — only for Thor, in borrowed iron gloves, to catch it and hurl it back through the giant himself.