Sigurd Snake in the Eye was one of the sons of the legendary Danish king Ragnar Lothbrok. His mother was Aslaug, daughter of Sigurd the Slayer of Fafnir. Sigurd was born with a mark in his eye described as Ouroboros (a serpent biting its own tail). Among his brothers were Björn Ironside, Ivar the Boneless, Halfdan and Ubbe.
There is now speculation that the mark in Sigurd's eye is the result of a congenital mutation of the Pax6 gene.
In his youth Sigurd was close to his father. He later lived for some time in Scotland and the Shetland Islands.
In 865 King Aella II of Northumbria defeated, captured and killed Ragnar Lothbrok by throwing him into a pit of snakes. Sigurd and his brothers received news of their father Ragnar's death from King Aella's messengers to Denmark.
Sigurd the Snake in the Eye held a knife and clipped his nails as this news was told, and listened so attentively to the story that he did not notice the knife sticking into his bone and did not even flinch.
His brother Bjorn Ironside clutched the shaft of the spear with his hand and gripped it so tightly that the traces of his fingers remained. When Aella's ambassadors had finished their story, Bjorn shook the spear so hard that it broke in two.
Ragnar's sons swore to avenge their father's murder. According to the saga of Ragnar and his sons, the brothers gathered a small force and sailed to England.
In 866, Ragnar's sons led a large Danish army across the North Sea into England. At the battle of York, King Aella II of Northumbria was defeated, captured, and put to death with the Blood Eagle.
According to Ragnarssons Saga Sigurd the Snake-in-the-Eye was killed in battle with the King Ernulf.
The Ragnarssons saga reports that after the death of his father Ragnar, Sigurd the Snake-in-the-eye inherited Zealand, Scania, Halland, the Danish islands and Viken. He married Blye, daughter of King Ella of Northumbria. They had two children: a son Hardaknut and a daughter Aslaug.
Sigurd's daughter Aslaug became the wife of Helga the Bold (a descendant of King Hringarika) of the Dögling dynasty. They had a son, Sigurd the Deer, who married Ingeborg, daughter of King Harald Kluck of Jutland.
Sigurd and Ingeborg had a son Guttorm and a daughter Ragnhild. After the death of his paternal uncle Frody, king of Hringariki, Sigurd the Deer went to Norway and became king of Hringariki.
The Ragnarssons Saga reported that the berserker Haki of Hadaland killed Sigurd the Deer in battle and captured his children Ragnhild and Guttorm. But in the battle with Sigurd Haki lost his right arm and received three more wounds.
With his prisoners and loot, Haki returned to Hadaland. Haki then recovered from his wounds and decided to marry the 15-year-old Ragnhild.
At that time, the King Halfdan the Black, ruler of Vestfold (c. 820 - c. 860), organized an attack on Hadaland, as a result of which Ragnhild and her brother Guttorm were released from captivity. Ragnhild became the second wife of Halfdan the Black and the mother of Harald Fairhair, the viking who united Norway.