Post-Thor: The Dark World Theory
Loki Fed Odin to Fenrir
An old man’s fear of his inevitable death led Odin to chain Loki’s son, Fenrir, with the use of guile, and while Odin’s son, Tyr, lost a hand in the process, the wolf was chained with a sword put in his jaws to keep them open—in order to prevent the wolf from further biting. Loki thought it a fitting end to lead Odin through the dark and narrow passageways through the realms only to end where his son was chained. In removing the sword with swiftness, and hiding his wolf son with magic so Odin would not see him, Odin did not even have a chance to cry out before the wolf had him; the first taste of flesh for Fenrir in thousands of years was that of the one he was fated to end at Ragnarök. Fate had a strange way of working out to be true, no matter how hard one tried to fight it.
However, Loki, now king, understood how dangerous Fenrir is. If he were to keep the peace, his son would have to remain chained, lest his own rule in Odin’s name be questioned. The wolf must be tamed, and yet can never be, and so will never be freed… at least by Loki.