Gleipnir is the rope that used to bind Fenris Wolf.
The Norse Gods commissioned the dwarves to forge a chain that was impossible to break. The dwarves fashioned the chain out of six supposedly impossible things:
- The sound of a cat's footfall
- The beard of a woman
- The roots of a mountain
- The sinews of a bear
- The breath of a fish
- The spittle of a bird
Gleipnir's hold on Fenrir had weakened to the point where the Wolf was almost free. Magnus Chase managed to replace Gleipnir with a new rope after it was cut by his own sword Sumarbrander.