Shared with you
Rollo was based on a real Viking called Hrolf (latinized as Rollo) who went on to conquer parts of France. Those parts are now known as Normandy: "Land of the Norsemen". Hrolf was the ancestor of William the Conqueror. Actually being William's Great-Great-Great Grandfather.
The Norse people did not actually refer to themselves as Vikings as an ethnic or national identity. Viking was a profession and was the term for the act of raiding across the sea or a person participating in such an activity.
When Marco ilsø (Hvitserk) and Alex Høgh Andersen (Ivar) were cast in the series they weren't allowed to tell anyone, so they wrote to each other that they didn't get the role.
Ravens appear prominently in the series. Ravens had great cultural and religious importance in ancient Norse society, as they were seen as the agents of Odin who was said to own two ravens: Hugin (meaning "Thought") and Munin (Memory) who flew around and gathered information for him. One of Odin's many nicknames is Hrafnaguð, which means "Raven God". Vikings would carry banners depicting ravens. Ragnar's forces carry such banners. As such, the pagan characters in the series are likely to believe that when ravens appear, they are watched by Odin.
The name "Ragnar" means "keeper of the fort."
Ivar the Boneless was a real historical figure. The Vikings had a habit of sometimes giving ironic or teasing nicknames. Ivars nickname 'Boneless' may be referring to the fact that he sailed far(England and up the Russian rivers) and therefore never walked anywhere. In Scandinavian languages the same word is used for legs and bones so the English translation of Ivars' name could be both 'legless' and 'boneless'.