How is Assef represented in the novel?

Over the course of the novel, Assef changes little, as he progresses from the ultimate bully to the most ruthless of soldiers. As a child, he led the local gang. He was responsible for Hassan's rape, an act of domination. As an adult, he uses his power as a soldier to continue his despicable behavior. Hassan is dead, but his son Sohrab, is held and abused..... repeatedly. When Amir arrives to find the boy, he is beaten without remorse. Assef enjoys dominating those around him and takes pleasure in inflicting pain and humiliation.