Research Notes:

According to legend, Ragnar was thrice married: to the shieldmaiden Lagertha, to the noblewoman Þóra Borgarhjortr, and to Aslaug. Said to have been a relative of the Danish king Gudfred and son of the Swedish king Sigurd Hring, he became king himself and distinguished himself by many raids and conquests until he was eventually seized by his foe, King Ælla of Northumbria, and killed by being thrown into a pit of snakes. His sons bloodily avenged him by invading England with the Great Heathen Army...

As a figure of legend...the extent of Ragnar's historicity is not quite clear.

In her commentary on Saxo's Gesta Danorum, Hilda Ellis Davidson notes that Saxo's coverage of Ragnar's legend in book IX of the Gesta appears to be an attempt to consolidate many of the confusing and contradictory events and stories known to the chronicler into the reign of one king, Ragnar. That is why many acts ascribed to Ragnar in the Gesta can be associated, through other sources, with various figures, some of which are more historically certain. These candidates for the "historical Ragnar" include:

- King Horik I (d. 854),
- King Reginfrid (d. 814),
- a king who ruled part of Denmark and came into conflict with Harald Klak,
- one "Reginherus" who attacked Paris in the middle of the ninth century,
- possibly the Rognvald of the Irish Annals, and
- the father of the Viking leaders who invaded England with the Great Heathen Army in 865....

The medieval sources that cover Ragnar include:

- the Anglo-Saxon Chronicle, a collection of 9th-century annals,

- book IX of the Gesta Danorum, a 12th-century work by the Christian chronicler Saxo Grammaticus,
- the Tale of Ragnar's sons (Ragnarssona þáttr), a legendary saga,
- the Tale of Ragnar Lodbrok, another saga, a sequel to the Völsunga saga,
- the Ragnarsdrápa, a skaldic poem of which only fragments remain, attributed to the 9th-century poet Bragi Boddason,
- the Krákumál, Ragnar's death-song, a 12th-century Scottish skaldic poem. ¹