Regin

In the Icelandic legend, Regin was the son of Hreidmar and brother of Fafnir and Otter.

When Fafnir killed their father, he wanted the entire treasure for himself, so he drove Regin away. Not long after that, Fafnir was turned into a fearsome dragon.

Regin became Sigurd's foster father and tutor in Hjalprek's court in Denmark. He told Sigurd's story about his family and the treasure. Sigurd decided to help Regin in gaining the treasure. It was Regin who reforged Sigmund's shattered sword. Sigurd called this sword, Gram. With this sword, Sigurd killed the dragon.

Regin hoped to keep all the treasure, and tricked Sigurd that he would not seek vengeance upon the young hero if he cooked Fafnir's heart for him to eat. By eating the dragon's heart, Regin would become stronger than Sigurd. However, Sigurd discovered the deception when he tasted the dragon's blood and could understand the speech of the birds. The birds revealed the truth of Regin's intention, so Sigurd killed Regin and took all of the treasure.

In the Norwegian Thiðrekssaga, Regin was the brother of the smith Mimir. Here, Regin had been transformed into a dragon, while it was Mimir who was the foster father of Sigurd and made the sword Gram for Sigurd. However, Sigurd did not use the Gram to kill the dragon (Regin); instead, Sigurd used a large log that he had used to build a fire. With this wood, Sigurd struck dragon's head and killed Regin. Then Sigurd used his axe to chop off the dragon's head.

Sigurd, feeling hungry, cooked a bit of meat of the dragon in his kettle. Like in the Volsunga Saga, some of the juice (blood) of the dragon burned his finger. Sigurd immediately could understand the speech of the birds. Sigurd learned that Mimir had sent him into the forest to die. Sigurd ate the dragon's meat. Then Sigurd bathed in the dragon's blood, which made his skin hard and horny, invulnerable to all weapons except for the small part of his back which he could not reach.

Sigurd returned to his foster father with the dragon's head. Mimir knew the hero's intention to kill him for betrayal. Mimir promised to give him treasure and an invincible weapon to ransom his life. Mimir also revealed the wonderful horse at the castle of Brynhild. Mimir gave him armour, a helmet and the sword Gram. With the sword in his hand, Sigurd's lopped off Mimir's head. Sigurd took all the treasure within the smithy and left.