There is an oral source, which mentions Rollo and his ancestry. The source is one of the few surviving Old Norse poems recited by a woman, his mother. It tells the story of how a son of Rognvald Eysteinsson, Earl of Møre, in what is now Western Norway, was banished from his home by the king.
The poem is cited in the collection of sagas known as Heimskringla, attributed to the Icelandic poet and historian Snorri Sturluson (1178–1241). According to Chapter 24 of the Saga of Harald Fairhair, as translated by Samuel Laing (1844):
"One summer, as he [Hrólfr] was coming from the eastward on a viking's expedition to the coast of Viken, he landed there and made a cattle foray. As King Harald happened, just at that time, to be in Viken, he heard of it, and was in a great rage; for he had forbid, by the greatest punishment, the plundering within the bounds of the country. The king assembled a Thing, and had Rolf declared an outlaw over all Norway. When Rolf's mother, Hild heard of it she hastened to the king, and entreated peace for Rolf; but the king was so enraged that here entreaty was of no avail. Then Hild spake these lines: --
"Think'st thou, King Harald, in thy anger,
To drive away my brave Rolf Ganger
Like a mad wolf, from out the land?
Why, Harald, raise thy mighty hand?
Why banish Nefia's gallant name-son,
The brother of brave udal-men?
Why is thy cruelty so fell?
Bethink thee, monarch, it is ill
With such a wolf at wolf to play,
Who, driven to the wild woods away
May make the king's best deer his prey."
Rolf Ganger went afterwards over sea to the West to the Hebrides, or Sudreys; and at last farther west to Valland, where he plundered and subdued for himself a great earldom, which he peopled with Northmen, from which that land is called Normandy."
The line “Why banish Nefia's gallant name-son” refers to the fact that Hrólfr was named after his mother’s father, Hrólfr Nefja (the nose).
A better translation of ‘Gǫngu-Hrólfr’ would be ‘Walking-Rolf’, Rolf ‘who walked [away]’ or even Rolf ‘the Vagrant’. Gǫngu is a term that means «walking» or «the act of walking», as in the compound göngu-stafr («walking-stick»), but it could also mean «vagrant», as in the compounds göngu-kona («a vagrant woman») and göngu-maðr («a vagrant [man]») (Vigfusson 1869:191). There is no reference to the nickname in the original poem in Old West Norse, which means that it may have been given to him after he was banished, and could actually be a reference to the banishment. In the Codex Frisianus manuscript, the poem ends with the phrase “ef hann gengr til skogar” (“if he goes to the woods”), where “to walk” is the equivalent of “to go”, and the poem may thus have been the source of his nickname, which would have meant Hrólfr ‘who went [away]’ or Hrólfr ‘who left’.
Literature
Sturleson, Snorro. The Heimskringla, or Chronicle of the Kings of Norway. With a Preliminary Dissertation by Samuel Laing, Esq (Tr.). Longman, Brown, Green, and Longmans: London, 1844.
Vigfusson, Gudbrand. An Icelandic-English Dictionary. Oxford: Clarendon Press, 1869.
