Assef was a brutal bully with sociopathic tendencies even as a young teen in the opening chapters of The Kite Runner. He worshipped Adolf Hitler and hated the Hazara, and when the Russians took over Afghanistan and jailed many of the upper class, he grew to hate them as well. When Assef was terrorized in prison, he only learned to hate the Russians even more. The rise of the Taliban became the perfect outlet for him. The Taliban despised Russians, Americans and the Hazara--a trifecta that fit Assef perfectly. He wanted payback for his treatment by the Russians while in jail, and he never forgot his threat of revenge against Amir--now living in America. Unchecked murder and ethnic cleansing fit Assef's nature, and his intelligence and leadership ability probably helped his rise in the Taliban ranks.