Jasper Pääkkönen as Halfdan the Black, Harald's violent younger brother (part 1).Peter Franzén as King Harald Finehair, a Viking ambitious to become the first King of Norway.Alexander Ludwig as Bjorn Ironside, Ragnar and Lagertha's son and Torvi's husband.Gustaf Skarsgård as Floki, a gifted shipbuilder.Katheryn Winnick as Queen Lagertha, a shield-maiden and Ragnar's ex-wife she is the queen of Kattegat.Main article: List of Vikings characters Main