What role did assef play in The Kite Runner?

Bullying Amir and Hassan. He hated Hazaras like Ali and Hassan and like Hitler's extermination, believed in killing them all. In the end of the book, Assef is the man at the stadium in white with the sunglasses. He "owns" Hassan's son, Sohrab and sexual abuses him. Assef fights with Amir and Sohrab shoots his eye out with a sling shot. Amir and Sohrab escape.