Fafnir, in Nordic mythology, name of the great dragon slain by Sigurd, the Norse version of the German hero Siegfreid. As told in the Volsunga saga, Fafnir slew his father, Hreithmar, to obtain the vast amount of gold which Hreithmar had demanded of Odin as a compensation for the loss of one of his sons. Odin gave the gold but put a curse on it. Full of greed, Fafnir changed into a dragon to guard his treasure and was later slain by the young hero Sigurd. Sigurd was spurred on by another brother of Fafnir, the blacksmith Regin. Once Sigurd, under the advice of Odin, had killed Fafnir, Regin asked him to cook the dragon’s heart for him. Sigurd touched the heart as it was cooking to test if it was done and burned his thumb. He put his thumb into his mouth and was then able to understand the language of birds. (In this tale, knowledge is given to one who eats the heart of a dragon.) The birds told Sigurd that it was Regin’s intention to kill him, so instead Sigurd killed Regin and left with Fafnir’s treasure.