He was wrong for killing Sigurd, who was supposed to marry King Allae's daughter and become a king himself. Then after that, Sigurd's sons would become kings as well. They just killed one of the most useful characters in the story, who was blessed by Odin.
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Htsverk or Ubbe should've died since their story is kinda dull, when it comes to the histories.
On the other hand, I can relate with Ivar through his quick temper and personality, which is similar to mine. He represents the darkest side of me.