Fafnir was a European Dragon in Norse Mythology. Fafnir was originally a dwarf, the son of Hriedmar and brother of Otir and Regin, but got transformed into a dragon by the cursed ring Andvarenaut. Fafnir had stole a fortune given to the dwarves by the gods as a ransom for Otir's death, and the ring Andvarenaut was in the fortune. The ring then transformed him into a dragon, the living symbol of greed, that guarded his treasure to his death. He later died at the hands of the warrior Sigurd Fåvnesbane. Sigurd, urged on by Regin, cooked Fafnir's heart and consumed it, giving him useful wisdom (such as the fact that Regin wished to murder him.)
There are some later versions of the myth in which Siegfried, the hero of the German epic poem Nibelungenlied, is the slayer of Fafnir instead of Sigurd. These versions of the myth usually have Siegfried bathing in Fafnir's blood and becoming immune to harm afterward, aside from a single leaf-shaped spot on his back.
The Fafnir myth and Volsungsaga gave rise to the epic Ring Cycle of Wagnerian operas. This in turn inspired J.R.R. Tolkien, whose character of Smaug is not dissimilar to Fafnir.