The models of Sigurdur Fafnisbani (the killer of Fafnir) and Brynhildur, the wife of Gunnar, have been harder to find but it's assumed that the events related to the characters have some roots in the history of the "Mervikings" in France, in the 6th century, because their history is full of conspiracy, murders and machinations of women. But this evidence is not enough to be called historical basis for Atlakvida.

Jormunrekur, who is related to the characters later, after Atlakvida ends, is assumed to be the same man who is in Latin writings called Ermanrichus, the King of East Gots at the Black Sea. Judging from the records of that time he killed himself because he was so afraid of the Huns when they invaded Western Europe around the year 375. Gothic heoric poems say that he had been seriously wounded by Sarus and Ammius, who probably are Sorli and Hamdir (Gudrun's sons) revenging their sister Svanhildur (daughter of Sigurdur and Gudrun) that Jormunrekur had tortured and killed.

It can be interesting to compare the sequence of events in the heroic lays of the Poetic Edda to the time of the real events which are assumed to be related to the characters in Atlakvida. Then you will see that in the heroic lays time goes backwards compared to the real story:

If Sigurdur Fafnisbani is Sigibert in the story of the "Mervikings", like often is assumed, he was executed in 575 and Brynhildur in 614. After his death Gudrun married Atli/Attila who actually died in 453. After his death Gudrun had two sons, Hamdir and Sorli/Sarus and Ammius, who attacked King Jormunrekur/Ermanrichus in 375 or 78 years before they were even born! Some heroes!!!