In the "Elder Edda" the death of the Niblungs is laid to the charge of Attila; their sister Gudrun does her best to save them; when she fails in this, she takes vengeance for them on her husband.
In the German tradition, as in the version known to Saxo in the Nibelungenlied, in the Danish ballad of Grimild's Revenge (which is borrowed from the German), the lines are laid quite differently. There it is their sister who brings about the death of the kings; it is the wife of Sigfred, of Sigfred whom they have killed, that exacts vengeance from her brothers Gunther and Hagene. Attila is here put aside. Gudrun's slaughter of her children is unrecorded; there is no motive for it when all her anger is turned against her brothers. This shifting of the centre of a story is not easy to explain. But, whatever the explanation may be, it seems probable that it lies somewhere within the range of popular tradition, that the change is due to some of the common causes of the transformation of stories, and not to a definite and calculated poetical modification. The tragical complications are so many in the story of the Niblungs that there could not fail to be variations in the traditional interpretation of motives, even without the assistance of the poets and their new readings of character.
In some of the literary documents there may be found two kinds of variation from an original form of story,—variation due to those popular and indefinite causes, the variation of failing memory, on the one hand; and on the other, variation due to the ambition or conceit of an author with ideas of his own.
A comparison of the Atlakviða, the Atlamál, and the Lamentation of Oddrun may at first suggest that we have here to deal with just such variants as are common wherever stories are handed on by oral tradition. Further consideration will more and more reduce the part allotted to oral maltreatment, and increase the part of intentional and artistic modification, in the variations of story to be found in these poems.
All three poems are agreed in their ignorance of the variation which makes the wife of Sigfred into the avenger of his death. In all three it is Attila who brings about the death of the brothers of Gudrun.
It seems to have been a constant part of the traditional story, as known to the authors of these three poems, that Attila, when he had the brothers of Gudrun in his power, gave order to cut out the heart of Hogni, and thereafter to throw Gunnar into the serpents' den.
The Atlakviða presents an intelligible explanation of this; the other two poems leave this part of the action rather vague.
In the Atlakviða the motive of Attila's original hatred is left at first unexplained, but comes out in the circumstances of the death of the Niblungs. When the Burgundian kings are seized and bound, they are called upon to buy themselves off with gold. It is understood in Gunnar's reply, that the gold of the Niblung treasure is what is sought for. He asks that the heart of Hogni may be brought to him. They bring him, instead, the heart of Hialli, which Gunnar detects at once as the heart of a coward. Then at last the heart of Hogni is cut out and brought to Gunnar; and then he defies the Huns, and keeps his secret.
Now is the hoard of the Niblungs all in my keeping alone, for Hogni is dead: there was doubt while we two lived, but now there is doubt no more. Rhine shall bear rule over the gold of jealousy, the eager river over the Niblung's heritage; the goodly rings shall gleam in the whirling water, they shall not pass to the children of the Huns.
Gunnar was thrown among the snakes, and there he harped upon his harp before his death came on him. The end of Gunnar is not told explicitly; the story goes on to the vengeance of Gudrun.