In Norse mythology, Fenrir or Fenrisulfr is a giant wolf. It is the son of Loki and the giantess Angrboða. Fenrir was tied up by the gods, but was destined to grow too big for his bonds and eats Odin during Ragnarök. After killing Odin, he is killed by Odin's son, Viðarr.
This pendant is the head of Fenrir atop of one of his teeth.