In Norse mythology, the dragon who guards a cursed treasure and is slain by Sigurd is Fafnir.
Fafnir begins the story not as an ordinary dragon but as a dwarf or humanoid figure in the Völsung Cycle. Driven by greed, he kills his father, Hreidmar, and takes the ring and hoard of the dwarf Andvari. The treasure carries a curse, and Fafnir transforms into a dragon to guard it.
Fafnir’s brother Regin helps the hero Sigurd obtain the sword Gram and plots the dragon’s downfall. Sigurd hides in a pit beneath the path Fafnir uses, then thrusts the sword upward into the dragon’s underside. After tasting Fafnir’s blood, Sigurd gains the ability to understand birds, who warn him of Regin’s treachery.
The name is sometimes written Fáfnir or translated with varying spellings. Fafnir should not be confused with Jormungandr, the Midgard Serpent, or Nidhogg, the dragon associated with the roots of Yggdrasil. Lindwyrm is a general dragon type, not this specific character.