After faking his death in an attempt to infiltrate Paris in the season 3 finale, Fimmel said during the panel that the weakened King of Denmark will be "intrigued by death" when the show returns next year. "He's got very close to death," the actor said. "A lot of this year is his fascination with death. Like Odin, who hung himself to feel how it felt to be dead."
Hirst further explained Ragnar's season 4 storyline during his interview with The Hollywood Reporter, saying that even though Ragnar has managed to return to Kattegat after a fairly long journey from Paris, "he's still desperately ill -- he's at death's door."
Hirst added that "some of the early parts of next season are about the possibility of him dying and what are the ramifications of that. Who's going to rule and what will it mean if the great Ragnar Lothbrok dies now? It sets up all future possible conflicts about the consequences of him dying. You can see the people cueing up to claim power.