How has Amir's character evolved in The Kite Runner?
During his childhood in Kabul, Amir grows up under the dominating hand of his father, Baba. Baba is a physically impressive man, and he is disappointed with Amir's introspective personality. Amir shuns sports and allows Hassan to fight his battles for him, a fact of which Baba is both aware and embarrassed. Amir consequently has little confidence in himself except for his imaginative writing skills, which Baba disdains. Amir also resents the attention that Baba shows Hassan, and he plants evidence which appears to show that Hassan has stolen from the family. Amir had previously refused to come to Hassan's aid when he was raped by Assef, showing a cowardice of which Amir was ashamed.
These two misdeeds against Hassan haunted Amir long after he and Baba moved to California. Although Amir and Baba's relationship improved considerably in America, Amir could never forgive himself for the deceitful acts. Even after his marriage to Soraya and his success as a writer, Amir was ashamed of his past in Afghanistan.
However, as Rahim Khan tells him, "there is a way to be good again," and Amir summons the courage to return to his homeland and find Hassan's missing son. He successfully brings Sohrab back to America and realizes at last that he has atoned for his past sins. He stands up to the Taliban and to General Taheri and, in a last token act of respect for Hassan, Amir offers to run the kite for Sohrab--just as Hassan had done so many times for him.