Jason represents the modern bourgeois order that came to replace the patriarchal past of the American South. This is the most down-to-earth character of all that appears in the book; he has a sober way of thinking and cold calculation in all things that surround him. As a child, Jason showed a healthy craving for money — he glued kites for sale. Now he works as a clerk in a city shop. His money, certainly, interests him much more than family, he puts the real side at the head of all relations. At the same time, he is in his own way possessing an obsession with his sister.
Caddy’s boyfriend — the young banker, promised him a place in his bank. When Caddy left home, this opportunity becomes impossible. Jason takes her daughter Quentin from her and defames her name in every way.
He appropriates the money sent by Caddy to her child, destroys her letters and seeks to send his mentally ill brother Benjy to the mental hospital. He is the only character who is able to stand up to his mother because he can be just as manipulative and passive-aggressive as she. In the person of Jason author draws the most disgusting character: he is a mean, low, greedy man who always tries to hide his own insolvency behind his fake importance. Jason personifies the moral and material decline of the Compson family.
Jason Compson IV in the Essays