Gleipnir was the third of three magical chains forged by Brock the dwarf and his brother Sindri. The first was Laeding; the gods got Fenris to try it on and he broke through it right away. The second chain was Droma; Fenris also broke it with little effort.
The third chain, Gleipnir, was forged from six impossible and poetic sounding ingredients, which vary slightly from story to story:
- the footfall of a cat
- the roots of a stone (or a mountain)
- the beard of a woman
- the sinews of a bear (I don't get this one. Don't bears have sinews?)
- the spittle of a bird
- the breath of fish
Gleipnir was thin and soft as a silk cord. When the gods bet Fenrir he couldn't break it, he was (rightly) suspicious, and would not allow himself to be bound unless a god would put their right hand in his mouth. Tyr the swordsman let his hand be the sacrifice, and the terrible wolf Fenris was bound until Ragnarok.