Draugr

The Draugr is one of the Undead, a creature from Viking folklore, renowned for its terrible strength and its insatiable hunger for human flesh and blood. This creature is virtually immune to the weapons of man, and must be wrestled into submission, and then decapitated by a blade forged of cold iron. The body must then be burnt to ashes. This creature is a shapeshifter, taking the form of a raven, a wolf, or a wisp of smoke to travel in search of its prey (it resembles the classic Vampire in this regard). Even though the Vikings were fierce and almost maniacal in battle, they feared this creature more than anything else. Only a true hero could destroy it once and for all.