Creator Makoto Yukimura has cited the series Berserk as an inspiration, the manga has also been compared to Berserk in many ways.
Askeladd's backstory is based on the early life of Olaf the Peacock, a major Icelandic chieftain and character of the Laxdoela Saga.
Thorfinn is loosely based on a real life Viking, Thorfinn Karlsefni Thordarson, one who had been part of Leif Eriksson's expedition and has direct family ties to Ragnar Lodbrock
Bjorn/Björn means bear in the Scandinavian languages and is a name often associated with vikings. Furthermore the character is referenced to be a berserker, who are in the sagas said to either literally in fighting fury to transform into bears or fight with the ferociousness of a bear. Berserker translates as "bear-shirt/coat" and these warriors were often depicted wearing a bearskin.
Canute's complicated relationship with his father Sweyn could be seen as tragic in hindsight: the medieval chronicles attribute Sweyn as having been abused by his own father Harald I, aka Harald Bluetooth. Emma of Normandy, wife of Canute, reported in her biography Encomium Emma Reginae that Sweyn was hated by his father.