In Norse mythology, Gleipnir (Old Norse "open one")[1] is the binding that holds the mighty wolf Fenrir (as attested in chapter 34 of the Prose Edda book Gylfaginning).
The Gods had attempted to bind Fenrir twice before with huge chains of metal, the iron chains of Leyding and Dromi, which Fenrir had torn apart.
Therefore, they commissioned the dwarves to forge a chain that was impossible to break.
After the gods failed to bind the demon wolf twice in a row, they asked Freyr's messenger Skírnir to find the strongest ropes made by the dwarves.
Gleipnir is said to hold until Ragnarök, when Fenrir will finally break free and devour Odin.