Moddan Moddansson of Dalr, Mórmaer of Caithness - Probably Fictional

So that's a book, published in 1848, translated into English from Irish from Latin. And the quoted section is the translator's personal note and opinions.

"Karl = Macbeth" is one of the *earliest* and *most obvious* interpretations, but it hasn't held up all that well,

"It is recorded by the Northmen that , at this same epoch of the second Malcolm’s death , one Karl Hundason “ took the kingdom ! of Scotland , ” that is to say , assumed the style of ardrigh ; and they appeal to the contemporary and undeniable authority of the Orkney bard , Arnor Jarlaskald , of whose poems the authenticity will hardly be questioned . He appeared as king of Scots in Caithness , supported by the forces of an Irishman acting in Caithness , named Moddan of Duncansby , and called " brother ( in the sense , I suppose , of brother - in - law ) to the king of the Scots , whom Karl appointed to be his general , and , on Thorfinn's refusal of tribute , to be Jarl of Katanes . He appears to be described as cousin german of Karl . But in various actions Moddan was defeated , and slain , by Thorfinn Sigurdson ( daughter's son to Malcolm II . ) , and by his tutor , Thorkell - Fostri ; and Karl , equally unsuccessful in his own subsequent efforts , disappeared from those parts , and his fate was never ascertained .-- Orkneyinga Saga , p . 31. Karl's forces , besides those from Ireland , were raised both in East and West Scotland , and especially in Cantireº . He was son to Hundi , i . e . Canis , otherwise Hvelpr , i . e . Catulus . Sigurd
Sigurd , before marrying that king's daughter , had defeated the two Scottish jarls , Hundi and Melsnaddi or Melsnata ” ( Maelsnectai ) , not far from Duncansby , and slain the latter . See Nial's Saga , cc . 86 , 87. This Hundi should be Karl's father . Sigurd also himself had a son Hvelpr or Hundi , whom Olaf son of Tryggvi took to Norway as a hostage , and christened Hlodver . These events happened from twelve to thirteen years after Finleg's death ; and when Karlº was quite in his youth , for Arnor Jarlas kald , Earl Thorfinn's bard , says of him and the war he carried on ,

“ Ungr olli ' thvi theingill , ” “ The youthful king was the cause thereof . "

"Therefore Karl coincides with Macbeth in these points : in his probable age , in that he was a claimant of the crown on Malcolm's death , that he did not then succeed in his claims , and that he is not averred to have perished in the attempt . But he differs in the names , Karl Hundason being very different from Macbeth Mac Finleg . The difference however is evanescent ; for the Norse word Karl is no more of a Scoto Pictish name , than Philadelphus or Soter were Coptic names . And the Norse word Hundi was not any name at all , but a nick - name , being given ( both to this Celt , and to Hlodver Sigurdson ) in the alternative , Hvelpr edr Hundi , Hundi etha Hvelpr , anglicè , “ either hound or puppy . ” We chiefly , if not solely , meet with it for a names in Orkney and Caithness ; and perhaps it was adopted from the Gaelic appella tion by which alone a king of Scots of the tenth century ( a vile person , but whether so called on that account I do not say ) is known to us , Culen or Catulus . "

"Vide Olaf . Trygg . cap . xcviii . tom . i . p . 202 , ed . 1825 ; et ap . Snorro , cap . xi . p . 145 ; Torfæi Orc . 1 , cap . x . cap . xiii . Considering the synchronism of Simeon Dunelmensis ; that Malcolm II . could scarcely have any claimant of his inheritance named Karl , otherwise than through his daughter , Sigurd's wife ; that no idea of a Norse claim to the succession , through Sigurd , is anywhere hinted ; and that the right and might of such a claim , had it been raised , would have been with Malcolm's grandson , the valiant Thorfinn Sigurdson , Earl of Orkney and Katanes ; I am induced to the belief , that Macbeth in his youth was known in the northern jarldoms by the Teutonic appellation of Karl , man , and that his father , Finnleikr Jarl , who fled before Sigurd Hlodverson at the Skidamyri ,

Skidamyri , was likewise the Hundi Jarl , dog , whom the same prince defeated , also in Caithness ; the son's title standing in favourable antithesis to the father's . Finleg did not fall by northern hands , neither did this Hundi or Hvelpr ; and Maelsnectai , the name of this Hundi's colleague in the war , was a name used in the house of Ruadri ."