Regin

Reginn, often Anglicized as Regin, in Norse mythology, was the son of Hreiðmarr and foster father of Sigurd. His brothers are Fafnir and Ótr. When Loki mistakenly kills Ótr, Hreiðmarr demands to be repaid with the amount of gold it takes to fill Ótr's skin and cover the outside. Loki takes this gold from the dwarf Andvari, who curses it and especially the ring Andvaranaut. Fafnir kills his father for this gold, and Regin gets none of it and becomes smith to the king. He eventually becomes Sigurd's foster father, and teaches him many languages as well as sports, chess, and runes.

Regin had all wisdom and deftness of hand. Of his two brothers, he has the ability to work iron as well as silver and gold and he makes many beautiful and useful things. While Sigurd is living with Regin, Regin challenges Sigurd's respect in the kingdom. He tells Sigurd to ask for a horse. Sigurd asks the advice of an old man in the forest, and the old man shows him how to get a horse that is descended from Sleipnir, the eight legged horse of Odin. Regin continues to goad Sigurd, this time into killing Regin's brother. He offers to make a sword for Sigurd, but Sigurd broke every sword Regin forged for him by striking at an anvil. Sigurd retrieves the broken pieces of his father Sigmund's sword, Gram, and brings them to Regin. Regin repairs the sword and gives it back to Sigurd. When Sigurd again tests the blade by striking the anvil, the anvil this time is split down to its base, and when Sigurd places a piece of wool in a stream, the current pushing the wool against the sword was enough to cause the blade to cut it in two. Sigurd is finally very pleased with Regin's repaired weapon.

After using Gram to kill Fafnir, Sigurd returns to ask Regin what to do. Regin instructs him to roast the heart of Fafnir, his brother, and let him eat it. As juice from the dragon's heart foamed out, Sigurd tested it with his finger to see if it was done cooking. As the blood touches his tongue, Sigurd understands the speech of birds, who warn him that Regin will kill him. Before he lets any of this happen, Sigurd first wields Gram and cuts off Regin's head.

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

In the operatic cycle Der Ring des Nibelungen, by Richard Wagner, the role of Regin is played by the Nibelung dwarf Mime, brother of Alberich (the Nibelung who forged the cursed ring out of the Rhinegold). Except for the change in name, probably inspired by the Thidrekssaga, the story of Regin, Sigurd and Fafner in Wagner's opera Siegfried follows closely the text of the Eddas.