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In 869 we have an event which rapidly achieved almost mythic status in English Christian folklore: the horrible martyrdom of King Edmund of East Anglia by the appalling Ivar the Boneless, who according to some traditions brought a great Viking army to England in pursuit of revenge for the killing of his father, the semi-legendary Ragnar Lothbrok, executed by the king of Northumbria.
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Heather O'Donoghue (From Asgard to Valhalla: The Remarkable History of the Norse Myths)
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Ragnar Lothbrok, the famous Viking, is still a mysterious historical figure, hidden in myths and links to a few chieftains. He was the father of legendary figures such as Ivar the Boneless, Halfdan Ragnarsson, Bjorn Ironside, Sigurd Snake-in-the-Eye, and Ubba.
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Noah Brown (Ragnar Lothbrok and a History of the Vikings: Viking Warriors including Rollo, Norsemen, Norse Mythology, Quests in America, England, France, Scotland, Ireland and Russia [3rd Edition])