Ragnar’s brother in the tv series. As we just are seeing he becomes the founder of Normandy and ancestor of William the Conquerer.
Rollo did exist.
If Ragnar did exist, he probably existed a century earlier.
I remember the Ragnar in the 1958 Viking movie . Though a prisoner he was able to die fighting, with a sword in his hand, when he leaped into the dog pit, Valhalla bound.