In Norse mythology, Fafnir was a son of the dwarf king Hreidmar and brother of Regin and Otr. In the Volsunga saga, Fafnir was a dwarf gifted with a powerful arm and fearless soul. He wore the Aegis helmet and guarded his father's house of glittering gold and flashing gems. He was the strongest and most aggressive of the three brothers.

After Otr was killed by Loki, Hreidmar received the cursed gold of Andvari's as repayment for the loss of his son. Fafnir and Regin then killed their father to get the gold, but Fafnir decided he wanted it all, turning into a dragon (symbol of greed). Regin then sent his foster-son, Sigurd, to kill the dragon. Sigurd succeeded, but then killed Regin too, upon learning that he had planned to kill him once he had recovered the gold.

As Fafner, he featured in Richard Wagner's Der Ring des Nibelungen.