Regin

In Norse mythology, Regin was the son of Hreidmar and foster father of Sigurd. Regin and his brother, Fafnir, killed Hreidmar for the cursed gold he had received from the gods after they killed his other son, Otter. Fafnir, however, turned into a dragon because he wanted to keep all of the gold (dragons frequently symbolize greed in European folklore). Regin sent Sigurd to retrieve the gold.

Regin forged a marvelous sword for Sigurd, but it quickly broke. Sigurd found his father's (Sigmund) sword, Gram, and had it fixed and reforged by Mimir and used it to kill Fafnir. He gained wisdom from licking the dragon's blood because Fafnir could talk to birds. Sigurd, who had discovered that Regin was planning on killing him to get the gold from the birds, killed his stepfather and took the gold.

The Thiorekssaga relates a slightly different tale, with Regin as the dragon and Mimir as his brother and foster father to Sigurd.