Ragnar Lothbrok (Travis Fimmel) will die at some point when "Vikings" Season 4B premieres sometime this fall. As a result, his sons are already staking their claim on the Danish throne.
Rollo (Clive Standen) and the Parisians defeated King Ragnar in the first part of Season 4, making him flee. However, after reaching Kattegat, Ragnar will discover how his defeat disillusioned his people to the extent that they lost faith in their king.
When Season 4 returns, Ragnar will confront his sons and other villagers, daring them to kill him and take the throne from him. While all the sons wish to have the throne, it is rumored that Ivar the Boneless (Ales Hogh Andersen) will stand the high chance of becoming the King of Kattegat because he is immensely strong.
In the absence of Ragnar, Ivar is the only son who still believes in his father, something that gives him an added advantage to become the heir. "Vikings" Season 4B will apparently shift focus towards the brothers, revealing how far they are willing to go just to have power.
Andersen had an interview with IGN, wherein he shared what sets his character besides his older brothers. The actor believes Ragnar is very clever.
"It doesn't take him that much time before he realizes that, because of the crippled Ivar, because of the past and because of his entire life as a cripple in an environment that does not embrace it," Andersen said. "He's the toughest one of them all."
The other three actors who play Ivar's brothers concur, indicating that he is the "most Viking" among the siblings. Although Ivar is the youngest among the brothers, they will look for the Viking he is and his strong will.
In a statement via Vikings Season 4 community forum, Ubbe (Jordan Patrick Smith) said that Ivar has one of the biggest disabilities one can ever have as a Viking. He is crippled but he is still brilliant enough and strong enough to keep going.
Watch out for "Vikings" Season 4B when it returns this fall to discover what happens with the Kattegat Kingdom. Here is footage for more information on the upcoming second part of Season 4: