Fafnir

Dragon. Fafnir was the son of Hreidmar, and brother of Regin and Otter.

Originally, Fafnir was a human who was able to shape-shift. Fafnir gained possession of the treasure after killing his father. He drove his brother (Regin) away by changing himself into a dragon.

The hero Sigurd killed Fafnir. Since his blood and heart contained magical properties, Sigurd ate his heart. That gave him greater strength and the blood allowed him to understand the language of the birds.

(See Otter's Ransom and Sigurd, Fafnir's Bane in the Völsunga Saga, for the full story).

According to the Norwegian Thidrekssaga and other German epics, the dragon that Sigurd or Siegfried killed was named Regin, while the dragon's human brother was a smith named Mimir. The name Fafnir was ignored in these tales.