Tyr's defining deed is an act of deliberate self-sacrifice unique among the gods. When the Aesir resolve to bind the monstrous wolf Fenrir, whose growth threatens them all, with the magical fetter Gleipnir, the wolf, suspecting a trick, agrees to be bound only if one of the gods will lay a hand between its jaws as a pledge of good faith. Tyr alone is willing, and when the binding holds and the wolf finds itself trapped, it bites off his hand at the wrist. The story, told by Snorri, makes Tyr the god who keeps faith at a personal cost for the safety of all, and gives Norse myth its clearest image of justice bound up with sacrifice: the pledge was made in bad faith, and Tyr pays for the community's necessary deception with his own hand.
Very few images of Tyr survive from the Viking Age, but two stone monuments are widely read by scholars as depicting his defining myth. The tenth-century Gosforth Cross in Cumbria, England, carved after Norse settlers had brought their traditions into Christian Britain, shows a figure with one hand thrust into the mouth of a great beast, generally identified as Tyr and Fenrir, standing alongside explicitly Christian imagery on the same monument, a striking case of pagan and Christian symbolism carved side by side. The Swedish Ledberg stone carries a comparable scene. Such finds are rare enough that most of what is confidently said about Tyr still rests on the written Eddic sources rather than on surviving pictorial evidence.