Ivar Ragnarson (the boned or boneless) was the son of Ragnar Lothbrok unlike his legendary progenitor the existence of Ivar is an established historical fact he would have been born around 794 and died around 872 in Dublin from a "sudden and hideous" according to the monks of the time.
A Viking grave discovered in 1686 at Repton in Derbyshire may be that of the boneless Ivar. The burial mound contained the remains of 200 warriors and 50 women which would indicate the high rank of its "tenant".
Ivar is said to have ruled over parts of present-day Denmark and Sweden in 855 he sacked East Anglia (along with his brothers Ubba and halfdan)
in 856 he took York from the Northumbrians. In 865 the three brothers conquered the Danelaw seeking to extend to the rest of England but they were opposed in their project by Alfred the great king of Wessex.
Ivar had the reputation of being a "berserker" a mad warrior. In 869 according to "the Latin passion of King Edmund" written by Abbo de Fleury, Ivar had King Edmund of East Anglia executed in the same way as St. Sebastian in the nave of a church attached to a column there would have served as a target for archers until death followed (legend says that having heard of the miracle of St Sebastian, the Vikings would have liked to see it firsthand (it worked less well for Edmund than for its predecessor apparently).
The Ragnarson brothers would also have executed King Aelle of Northumbria by subjecting him to the ordeal of the blood eagle to avenge their father Ragnar Lothbrok thrown into a snake pit by Aelle a few years earlier.
there is no further mention of Ivar in the records after 870.
Ivar the Boneless is a recurring secondary character in Uthred's excellent cycle of Bernard Cornwell's fictionalized (but grounded) chronicle of the reign of Alfred of Wessex.
C.L.