Fafnir was a giant in Germanic mythology who, along with his brother Fasolt, built Valhalla. In exchange, they asked for the goddess Freyja in marriage. Odin offered them gold instead, and Fasolt accepted it. Fafnir kiled his brother to get all of the gold for himself, and in order to better guard his treasure, transformed himself into a dragon. He was killed by Sigurd on Glistenheath. By eating Fafnir's heart Sigurd gained the ability to talk to and understand birds.