Ragnar Lothbrok (played by Travis Fimmel) famously toed the line between the Norse traditions and beliefs and the Christian teachings brought to him by Athelstan (George Blagden).
However fans of the show seem to believe Ivar the Boneless (Alexander Hogh Andersen) could be the next character to jump between religions.
Fans of the show will recall the final episode of season five saw the tyrant escaping to Russia to escape the wrath of his brother, Bjorn (Alexander Ludwig).
This means Ivar may be surrounded by a number of historical figures who are Christian.
Religious differences have always been at the core of Vikings, and this change of scene for Ivar could place him in a tricky situation.
While he has always stayed true to the Norse religion, he has also blasphemed a little by announcing himself as a new god.
With everything he has ever known now gone, he may be seeking a new redemption now his armies and family have deserted him.
This theory coincides with the ongoing theory that Ivar is most similar to Ragnar out of all his children.
And, as fans remember, Ragnar held a soft spot for the Christian religion after befriending Athelstan.
Could this final conversion land Ivar the army he needs to overthrow his brother once and for all?
Meanwhile viewers have been theorising over the possibility of Ragnar returning to the show.
This thought sparked after a number of viewers began pointing out the poster for season six shows Ivar being crowned by an unknown person in shackles.
They then suggested these hands could be Ragnar’s – as they look similar to when he was killed off back in season four.
On the subject one fan said: “I think maybe Ragnar will come back from the dead.”
While another quizzed: “Did anyone see Ragnar’s body?”
Fans also pointed out Ragnar’s body was never found after his death – but does this mean the viking warrior will return?
And if so, will he take on his son Ivar for the crown of Kattegat?
Vikings season six is expected to return to History Channel and Amazon Prime Video this year.