As for the other two famous images, the blood eagle and the berserker—those are the result of mistranslations.
"It is likely that your son is going to make a berserker, Karlsefne," he answered.
Then in the Jam-wagon there awoke the ancient spirit of the berserker.
Conceive the Calls coming over in a dragon ship, filled with berserker rage, to ravage England and glut themselves with our blood.
In berserker madness, torrent and uproar, clashed the two colours.
Men of the berserker type, however, are more addicted to going straight through the lot.
But he was no match for the berserker rage which had transformed the man from the woods.
She is seized by a sort of berserker fury, throws herself upon her horse, cries to her hounds, and dashes off.
He believeth thee the slayer of Sikend the berserker from under the bridge.
As the mother on learning the tragic truth had taken refuge in a dead faint, so he took refuge in a berserker rage.
alternative form of berserk (q.v.), from Old Norse berserkr, accusative of berserk. This is the oldest form of the word in its revival in Modern English (1822), and perhaps Scott, who introduced it, mistook the -r for an agent-noun suffix. Further compicated because it has the form of the Old Norse plural, and English berserker sometimes is plural.
1844, from berserk (n.) "Norse warrior," by 1835, an alternative form of berserker (1822), a word which was introduced by Sir Walter Scott, from Old Norse berserkr (n.) "raging warrior of superhuman strength;" probably from *ber- "bear" + serkr "shirt," thus literally "a warrior clothed in bearskin." Thus not from Old Norse berr "bare, naked."
Thorkelin, in the essay on the Berserkir, appended to his edition of the Krisini Saga, tells that an old name of the Berserk frenzy was hamremmi, i.e., strength acquired from another strange body, because it was anciently believed that the persons who were liable to this frenzy were mysteriously endowed, during its accesses, with a strange body of unearthly strength. If, however, the Berserk was called on by his own name, he lost his mysterious form, and his ordinary strength alone remained. ["Notes and Queries," Dec. 28, 1850]The adjectival use probably is from such phrases as berserk frenzy, or as a title (Arngrim the Berserk).