Ivar The Boneless was the commander of the "Great Heathen Army" that invaded England in 865 in revenge for the killing of Ivar's father, Ragnar Lothbrok. He's a historical figure that I've found interesting mainly because his name. Why was he called "The Boneless"? It's something that historians haven't been able to answer.
He was carried into battle on a shield, supposedly because he was lame which leads most to conclude that he suffered from some degenerative bone disease. Another theory is that he was a dwarf with brittle bones disease. Some have said that Boneless could've been an ironic name given to a very tall person or it could've been a reference to Ivar being impotent. We may never know the truth, but maybe that's part of the attraction to this historical figure.
I came across this documentary a while ago and found it interesting, you get the feeling that the documentarians come up with the answers that they wanted to but it still brings up some interesting facts and theories.