Fáfnir (Meaning: the griffin) is a dragon figure of Norse mythology, which is recorded in the heroic song Fáfnismál of the Liederedda and in the Völsunga saga. The figure also appears as Fafner in Richard Wagner's opera.
According to the Icelandic Völsunga saga, Fafnir is the son of the dwarf king Hreidmar. His brothers are named Otr (also Otur) and Reginn. Fafnir is described as a gifted dwarf who, with the help of a powerful weapon and his fearless spirit, guards his father's house, which is decorated with precious stones and shines golden. He is the strongest and most aggressive of the three brothers.
Reginn tells Sigurd how the Aesir gods Odin, Loki, and Hönir, on one of their journeys, while fishing, encounter his brother Ótr, who resembles an otter by day. Loki kills the otter with a stone, and the three gods skin their catch.
The gods arrive at Hreidmar's dwelling in the evening and are happy to show off the otter's skin. Hreidmar and his two sons, who are present, immediately seize the gods when they recognize the remains of their brother. They hold Odin and Hönir captive, while Loki is to bring the wergeld, a kind of ransom.
The gold is to fill the Otter's bellows and his skin is to be covered with red gold. Loki accomplishes the task by procuring the cursed gold of the dwarf Andvari as well as the ring Andvaranaut, although Loki was entrusted that both the gold and the ring would bring death to its wrongful owner. Out of greed, because Hreidmar does not want to give his two sons any of the wergeld, Fafnir kills his father in order to seize all the gold.
Reginn flees and later becomes the mentor of his foster son Sigurd. Fafnir retreats to a cave in the wilderness on Gnitaheide, where he lies on his gold to guard it. Gradually he takes the form of a lindworm, with the Aegishjalmur - a helmet of terror that changes appearance - making his countenance even more horrifying.
Reginn swears revenge on his brother Ótr and encourages his foster son Sigurd to slay the dragon.
Reginn advises Sigurd to dig a pit under Fafnir's tail to wait there. When Fafnir slides over it to drink water by a stream, he would be able to plunge his sword, Gram, into Fafnir's heart. Reginn then disappears and lets Sigurd do the deed.
When Sigurd has dug the pit, Odin appears in the form of an old man with a long beard and advises him to make more trenches so that Fafnir's blood can drain away. He wants to protect Sigurd from drowning in the dragon's blood.
The earth trembles as Fafnir appears, spraying venom as he meanders toward the water. Sigurd, unfazed, stabs Fafnir in the heart with his sword Gram as he crawls across the pit, mortally wounding the Lindworm.
The dying dragon speaks to Sigurd and wants to know his name, as well as the names of his father and mother. He further wants to know who sent the hero to kill such a terrible dragon as him.
Fafnir realizes that his own brother Reginn is behind the conspiracy and predicts that Reginn will also cause Sigurd's death. Sigurd tells Fafnir that he will go back to the beast's lair to take the treasure.
Fafnir warns Sigurd that anyone who possesses the gold is doomed to die. However, Sigurd replies that all men must die once and that it is the dream of many to be rich until they die, so he will take the gold without fear.
Reginn returns to Sigurd after he has slain the dragon. Full of greed, Reginn plans to kill Sigurd after he has cooked Fafnir's heart for him.
By mistake, Fafnir's blood reaches Sigurd's lips when he tries to taste whether the heart is cooked, which gives him the gift of understanding the language of the birds. He learns from Odin's birds about Reginn's impending plan to kill him and thereupon beheads Reginn, eats Fafnir's heart, and drinks Reginn's blood.
In some versions, Sigurd takes not only the treasure, but also the swords Ridill and Hrotti, the helmet of terror Aegishjalmur, and the golden cloak of invisibility.