How is Sohrab different from the other characters, and how are these differences a function of what he has experienced?
Sohrab is the young son of Hassan and Farzana, who have been killed by the Taliban. Not only has he witnessed his parents' execution, but afterwards he was sent to a dismal orphanage where he is sexually abused by perverted Taliban officials, one of whom is the grown up bully Assef, who was responsible for raping Sohrab's father Hassan when he was a boy.
Sohrab is traumatized. The Taliban have made up his face with eye makeup, etc., and he whimpers around Assef when Amir finally locates the boy. When Amir takes Sohrab with him, and tries to get him a visa to go to the U.S., Sohrab tries to commit suicide when he learns that the visa will not be approved. Sohrab is an old soul in a young body. He tells Amir he is too tired to live - this is very sad - something that an elderly person might say, not a young boy. Finally Amir does take Sohrab to the U.S. to live with him and his wife Soraya, but Sohrab does not speak for an entire year, so disturbed is he. At the end of the novel, Sohrab is just beginning to show signs of healing.
Sohrab's character offers Amir some sort of redemption. In saving Sohrab and raising the troubled child, Amir can in some way make up for his cowardly treatment of Sohrab's father Hassan when Hassan and Amir were boys.