Another of Ragnar's middle children, Sigurd "Snake-In-The-Eye" never really amounted to anything.
Sigurd, again, was destined for great things as one of the legendary sons of Ragnar. After all, the real-world counterpart of Sigurd went on to marry and have many children with a daughter of King Ælla.
Like all of Ragnar's children, Sigurd was exceptionally skilled in combat but had one fatal flaw, teasing his little brother Ivar.
After the time skip to Season Four, where all of Ragnar's sons are grown up, Sigurd is reduced to a household bully. Most of, if not all of his scenes revolve around arguing or teasing Ivar over his inability to walk. The other brothers seemed to have accepted Ivar for who he is, while Sigurd can't help but pry and poke fun.
The show gives off the impression that Sigurd may have understood Ivar's vicious and often cruel persona hidden behind his friendly demeanour. However, it comes across as more likely that Sigurd's attitude and constant belittling is what drove Ivar away from his family in the first place.
In the end, this cost Sigurd his life, as one final public outburst resulted in Ivar launching an axe into his chest.