For most of the first 4 seasons on History Channel's Vikings, Ragnar proved himself to be one of the most violent and skilled warriors in the Viking hordes. However, that doesn't mean he didn't have challengers to his throne.
Ragnar's brother Rollo was a savage warrior who inspired fear and admiration in those who followed him. For all the battles he helped his brother win, Rollo's only reward was to be overshadowed. Ragnar had taken everything from him; his glory, the woman he loved, and even raised Rollo's son as his own. So it isn't any wonder that Rollo has done some pretty despicable things to break free from his brother's grip, as he attempts to make a name for himself.
Allied With Jarl Borg
Rollo's relationship with his brother has always been tumultuous. He has always struggled to find his place in a world that seems to be Ragnar's for the taking. Whether wrong or right, Rollo's jealousy of his brother has always been his driving force.
This internal struggle was what led to his first betrayal when Jarl Borg noticed Rollo's potential as a warrior and a leader, offering him a chance to stand on his own if only he would fight against his brother. Initially hesitant, Rollo finally agreed to fight on Borg's side.
Murdered Arne
When Ragnar was in the fight of his life against Earl Haraldson, Arne was one of Ragnar's most loyal supporters. Rollo fought side by side with Arne on many occasions against their shared enemies. Though, Rollo's past loyalties meant nothing to him when he took up arms against Ragnar and Kattegat.
During the battle, Rollo severely wounded Floki and ended up murdering Arne with a spear thrust to the stomach. Instead of just giving him a merciful death, Rollo held the mortally wounded Arne on the end of his spear for the participants in the battle to see.
Became Kattegat's Drunk
When Ragnar met him in battle, Rollo was unable to fulfill his obligations to fight for Jarl Borg. He placed his weapons on the ground and presented himself at the mercy of his brother.
Due to his love for Rollo, Ragnar forgave his brother for his transgressions. While Ragnar had forgiven his brother, it was hard for those in Kattegat to forget his betrayal. Rollo soon found himself to be a pariah among his former friends, causing him to turn to alcohol as a coping mechanism from all the pain and guilt he felt inside.
Abandons Siggy
Ragnar might have forgiven Rollo but that didn't mean he was welcomed. Rollo was going to self-exile himself but Siggy stopped him. She believed he was destined for greatness, possibly even to the point of being king himself someday.
She wished to serve by his side as his lover and wife. Yet, it was not to be, as Rollo did stay but soon found himself a husk of his former self. It was only when Rollo was allowed to travel to Francia that he returned to his past glory. Sadly, this decision led to him abandoning Siggy.
Burns Jarl Borg's Men Alive
When King Horik and Ragnar needed a third partner to join them in their quest to raid Wessex, Horik demanded it to be Jarl Borg. However, Ragnar's fury with Borg after his failed coup attempt had not relinquished.
Ragnar did agree to have Rollo speak to Borg to see if being allies was a possibility. While Rollo talked Borg into allying with them, once he and his men were in Kattegat, Rollo burned down the building they were staying in and, with his brother's assistance, murdered Jarl Borg.
Rollo Is Responsible For Athelstan's Death
Rollo was never a friend of Athelstan. He never trusted the Christian from the beginning, especially after seeing Athelstan conflicted between his Christian faith and his loyalty for Ragnar back in Wessex. So, when Rollo noticed Athelstan no longer wore his arm ring signifying his allegiance to the Norse gods, he alerted Ragnar and the rest of his brethren to the possible treachery.
While Athelstan showed no signs of betraying Ragnar, Floki – who never trusted the former priest – used this knowledge as a reason to murder Athelstan as he prayed.
Rollo Kills Viking Settlers In Francia
After the Vikings infiltrated Paris's walls and forced Emperor Charles to give a tribute to keep Ragnar from plundering the city, Rollo was left behind to ensure that Vikings kept a presence in Frankia.
However, once Ragnar sailed back to Kattegat, Emperor Charles offered Rollo his daughter and the title of Duke of Normandy if he would rid the kingdom of the Viking presence and fight on their side if Ragnar ever returned. Rollo agreed to the offer and shortly afterward led an assault that massacred the Viking men, women, and children that had stayed behind.
Defended Paris Against Ragnar
Rollo knew it was only a matter of time before his brother returned to raid Paris of its treasures and land. Therefore, he prepared the Frankish defenses to fend off a Viking attack, while also training the Frankish soldiers to fight against the heathen horde that would soon arrive.
Rollo proved to be a great asset for Emperor Charles as he knew not just Viking tactics but how his brother thought. With dreams of glory, Rollo paid little mind to betray his own kind. His new homeland was Frankia and he would defend it till his death.
Tried To Kill Ragnar
After learning of the massacre that took the lives of the Viking settlers in Frankia, Ragnar knew his brother had betrayed him. After forming a raiding party, Ragnar set off for Frankia where his greatest fears were realized when he saw Rollo heading the Frankish forces.
Unlike last time, Ragnar found Paris's defenses too strong to break through and, in the last battle to take the city, Ragnar found himself face to face with Rollo. This time both parties were willing to kill the other but before Ragnar could kill Rollo, he was forced to flee.
Aided Ivar Over Björn
After the dissolution of the Heathen Army, Ivar and Harald make an attempt against Kattegat, which is now in the control of Lagertha. Knowing he doesn't have enough manpower to overtake Kattegat, Ivar seeks to ally with Rollo, who reluctantly agrees, so long as Björn is spared.
When Ivar's forces arrive at Kattegat, the battle is on even grounds until Rollo's Frankish forces arrive turning the tide in Ivar's favor. Lagertha and Björn soon find themselves overrun and are forced to flee their homeland for Wessex. Thanks to Rollo's assistance, Ivar becomes King of Kattegat.