Throughout human history, from the Bible to The Lion King, storytellers have been fascinated by the idea of brothers (or sisters) murdering one another. The most notable case of this was the story of Cain and Abel from the Bible’s Book of Genesis.
Found in only the fourth chapter of Genesis, it is the first example of violent sin in the Bible. In the Christian tradition, it is the first murder. The story is found below, in Genesis 4:2-12.
Now Abel kept flocks, and Cain worked the soil. 3 In the course of time Cain brought some of the fruits of the soil as an offering to the Lord. And Abel also brought an offering—fat portions from some of the firstborn of his flock. The Lord looked with favor on Abel and his offering, but on Cain and his offering he did not look with favor. So Cain was very angry, and his face was downcast.
Then the Lord said to Cain, “Why are you angry? Why is your face downcast? If you do what is right, will you not be accepted? But if you do not do what is right, sin is crouching at your door; it desires to have you, but you must rule over it.”
Now Cain said to his brother Abel, “Let’s go out to the field.” While they were in the field, Cain attacked his brother Abel and killed him.
Then the Lord said to Cain, “Where is your brother Abel?”
“I don’t know,” he replied. “Am I my brother’s keeper?”
The Lord said, “What have you done? Listen! Your brother’s blood cries out to me from the ground. Now you are under a curse and driven from the ground, which opened its mouth to receive your brother’s blood from your hand.When you work the ground, it will no longer yield its crops for you. You will be a restless wanderer on the earth.”
The Lord tests Cain, and Cain struggles. He murders Abel out of jealousy, causing God to frown upon him and condemn him to a life of wandering. This established a history of fraternal violence in fiction. Fratricide (the murder of a sibling), has been written about constantly, establishing a tradition of Cain and Abel in literature. John Steinbeck’s East of Eden is a modern reinterpretation, suggesting that filial violence will recur throughout history.
Parallel to the Bible, there is the story of the foundation of Rome. This begins with two twin brothers, Remus and Romulus, being raised by a she-wolf. Romulus ended up killing Remus, and went on to found the Eternal City. In the Mahabharata, a story about feuding groups of cousins, there are Karna and Arjuna, who were born of the same mother but different fathers. In battle, Arjuna kills Karna, after both have made a vow to kill each other.
This idea of siblings killing, or at least fighting, other siblings has been a constant cultural mythology. Shakespeare used it several times. Much Ado about Nothing and King Lear both have warring siblings, but this is most notable in Hamlet. Claudius, as a means of taking the throne, has killed his brother Hamlet and married his wife. In a shameful soliloquy, Claudius laments for his soul, saying: “O my offense is rank it smells to heaven; / It hath the primal eldest curse upon ‘t, / A brother’s murder.” Here, Shakespeare clearly alludes to the story of Cain and Abel.
Being that Hamlet parallels Cain and Abel, then logically, so does The Lion King, which was (loosely) adapted from the play. Scar kills Mufasa because of his jealousy at Mufasa’s throne on Pride Rock.
This theme has several appearances in Game of Thrones. Renly asserts his claim for the throne, in an attempt to take it from Stannis, who should be the rightful inheritor. (Most younger siblings do these things out of envy, but Renly seems to just think that he would make the better king.) The Hound and the Mountain are also a great example of violent sibling rivalry. It is abundantly apparent that they hate each other, despite only fighting once. And if you believe the rumors, they might fight again.
(The operative difference her is that Renly and Stannis is a conflict that comes out of a Throne dispute, whereas the Hound just wants to bring the Mountain to justice and spites his brother for attacking him as a child.)
There was a great deal of this in The Last Airbender and The Legend of Korra. Most notably, we see the rivalry between Zuko and his sister Azula play out. In Legend of Korra, (without going into potential spoiler territory) there is the conflict between Tarlaq and Unalaq which encompasses the entire Water tribe.
Thor and Loki, as they are depicted in the Marvel Cinematic Universe are Cain and Abel analogues. There is a slight subversion, in that Thor, the one more prone to be violent is the favored child, and the younger one is the one who actually betrays the older. But still, the idea of who gets the throne is what propels the story.
And of course, this theme transcends to figurative brothers. Spurring a million memes, the dialogue of “He’s my friend Tony,” and “So was I” from the Captian America: Civil War trailer encapsulates this idea of people who were close growing apart. The graphic novel The Dark Knight Returns covers the deteriorating relationship of Batman and Superman (and is the basis for the upcoming Dawn of Justice) after years and years of amiably working the Justice League together. In Revenge of the Sith, the fight between Anakin and Obi Wan has a similar moment, in which Obi Wan says “You were my brother Anakin, I loved you.”
I think that the recurrence of this idea comes from a couple of places. Often, our siblings can be the hardest people to get along with. And, of course, jealousy and inheritance are also incredible motivators. But it’s more than that; it shows a primal fear that our blood will kill us. To be betrayed by our family is the ultimate betrayal.