Older Brother (mother!)

The Older Brother is an antagonist in Darren Aronofsky's 2017 psychological horror film Mother! (italicized as mother!). He was portrayed by Domhnall Gleeson.

mother!
While living with Him in a house located in the middle of nowhere, an elderly man arrives to the house one evening, confusing the house as a bed-and-breakfast hotel. After some initial hesitation, mother relents and allows the elderly man to spend the night. Sometime over night, Him holds the sickly man over a toilet, and covers a wound on his rib cage with his hand. The next day, the man's wife arrives, and makes herself an unwelcome guest at their home as well. Him is at first delighted by their presence as they were fans of his work, but when they accidentally break a crystallized object that Him valued, he demands them to leave.

Sometime later that evening, the couple's warring sons arrive to the house. As their father was dying, they quarrel with each other. Getting into a scuffle, the older brother grabs a doorknob from the house, and hits his younger brother with it, killing him. The older brother receives a mark on his forehead before seemingly being cast out of the house. Him returns to mother, informing that the man had died. Several people arrive to the house to mourn the loss of the younger son. However, this leads to further disdain by mother.

Symbolism
It goes without saying that there are several biblical allusions scattered throughout the film. Him represents Abrahamic God of Judeo-Christian belief, and Man and Woman represent Adam and Eve respectively. As such, it is no stretch to say that the brothers represent Cain and Abel. The Older Brother is Cain, and much like in the biblical account, the Older Brother overpowers and murders his younger brother. Also like Cain, God exiles him after he attempted to lie saying that he did not know where Abel was; before he was banished, God gave Cain a mark that would shield him if anyone tries to kill him.

Trivia

 * He is actually brothers with the actor who portrayed the younger brother in real life.