In Chapter 21, Amir finally sees Sohrab and realizes something about the Taliban official. What is it?
When Amir goes to meet the Talib official and attempt to get Sohrab, he discovers that the official is Assef. Amir and Farid see this figure at the stadium (where Zaman, the orphanage director, sends them because the Taliban has taken Sohrab), and Amir calls him "John Lennon" because of the sunglasses he wears. Obviously, from a distance, and with Assef's appearance hidden under the disguise, Amir has no idea this is Assef. He does know, however, that this man is intimidating and violent, as he has seen the man stone an adulterous couple to death at halftime in the soccer stadium. Going into the meeting with the official, Amir believes he may not come out alive.
Assef reveals himself to Amir when Amir comes to meet with the Talib official about Sohrab. He tells Amir he never forgets a face, and then Amir realizes this is Assef. The fight for Sohrab becomes more symbolic now because Amir is able to take direct revenge on the man who assaulted Hassan when they were all children. During the fight, Assef's head covering falls off and his blonde hair is revealed, bringing us back to the description of the young Assef in Chapter 5. Amir is able to atone for his sin of abandoning and betraying Hassan to Assef's abuse (in Chapter 7, after the kite fighting tournament), and even though he is critically injured, Amir feels cleansed and even laughs during the fight. This is one step on Amir's journey to redemption and it's only fitting that he, with some help from Sohrab and his slingshot, has to defeat Assef along the way.
Amir goes to rescue Sohrab and meets the Taliban official in chapters 21-22 of "The Kite Runner." It is at this time that Amir realizes that the Taliban official is the same bully from his childhood who beat up and raped Hassan. The official "removes his glasses, and Amir realizes the official is actually Assef. Assef says he can have Sohrab, but first he has to earn him."
Amir has come full circle and now will face the fear and demons he has run from his entire life. He will face Assef.