Who is Assef from The Kite Runner and what is their importance?

Assef is the local bully and tormenter in the village. He is the person who rapes Hassan: an event that will plague Amir for the rest of his life. Assef is a socio-path. He is impressed by Hitler. Although Hitler was unable to eradicate the Jews, Assef thinks he can eradicate Hazaras.