In Neil Gaiman’s book Norse Mythology, the god who loses a hand to the wolf Fenrir is Tyr.
The gods raise Fenrir as a dangerous wolf and attempt to bind him with magical fetters. Fenrir agrees to be bound only if one of the gods places a hand in his mouth as a pledge that the gods will release him if the chain proves unbreakable. Tyr accepts the risk.
When Fenrir discovers that the gods have deceived him, he bites down and severs Tyr’s right hand. Gaiman retells this episode in accessible modern prose while following the central events of the Norse myth.
Tyr is often associated with law, oaths, courage, and warfare. The story is sometimes confused with Ragnarök, when Fenrir breaks free and kills Odin. Tyr’s injury happens earlier, during the wolf’s binding, and it is Tyr—not Odin, Thor, or Heimdall—who loses the hand.