The sagas explain Ívarr's affliction as a wedding-night mistake: Ragnarr, warned by his prophetic bride Áslaug to wait three nights before consummating their marriage or risk a child born 'boneless,' could not wait. Ívarr arrived with cartilage where bone should be (carried on a shield rather than legs, the sagas insist) and yet grew into the sharpest strategist of his generation, the brother the others deferred to for cunning rather than muscle. Whatever the epithet actually described (some scholars read beinlauss as a garbled 'legless,' others as a euphemism for impotence, others as pure legend), the sources agree he compensated with a mind the battlefield couldn't out-plan.
In 865 Ívarr landed in East Anglia at the head of the mycel hæþen here, the Great Heathen Army, an invasion the Anglo-Saxon Chronicle records as history and the Norse sagas frame as filial revenge: King Ælla of Northumbria had supposedly thrown Ragnarr into a snake-pit, and his sons came to collect the debt. Ælla died under the sagas' favorite punishment, the blood-eagle, while King Edmund of East Anglia, refusing to renounce Christ or rule as a pagan's puppet, was, by later tradition, bound to a tree and shot through with arrows 'like a thistle full of prickles' before being beheaded; the Church made him a martyr-saint within a generation.
Ívarr then vanishes from English annals around 870 at almost the exact moment a Viking king named Ímar disappears from Irish ones, only for Ímar to resurface ruling Dublin, and historians increasingly suspect the two names belong to one man. If so, the boy born 'without bones' became the founder of the Uí Ímair, a dynasty that held Dublin, York, the Isle of Man, and the western Scottish isles for the next century, dying, per the Annals of Ulster, in 873, no longer a saga's cautionary birth-omen but the ancestor of kings.