Edgar Allan Poe's "William Wilson" is an allegorical short story about the struggle between mankind's dual nature, the moral conscience and the evil instinctive nature. Similarly, in To Kill a Mockingbird, Harper Lee juxtaposes the moral conscience with the instinctive evil nature. Hence, both works present stories concerning the battle between right and wrong.
Poe opens his story of mankind's dual nature, 'William Wilson," by having his narrator describe himself as having developed an archenemy in his childhood, and his battles with the archenemy continue into his adulthood. The narrator, calling himself William Wilson, describes his archenemy as looking exactly like him, dressing exactly like him, and as having his exact same name, birth date, and school enrollment date. The only difference between the narrator Wilson and the archenemy Wilson is that the latter speaks in a "very low whisper." The allegory becomes obvious when, as the narrator goes about his life, each time he performs or is about to perform a corrupt and evil deed, the archenemy Wilson mysteriously appears and either whispers words of admonishment or exposes his deed. By the end of the story, the narrator Wilson kills his archenemy Wilson, a deed that likewise makes the narrator "dead to the World, to Heaven and to Hope," showing us that it is really his conscience that the narrator has killed, and killing his conscience bars him from Heaven.
Similarly, in Lee's story, it can be said that Atticus and his sister Alexandra are character foils that often represent the will of the conscience and its antithesis. Atticus represents the will of the conscience because he is always doing as his conscience tells him to do, such as defending Tom Robinson, despite what his racially prejudiced society thinks he should do. In contrast, his sister Alexandra is very representative of the views of the Old South. Contrary to Atticus, Alexandra scorns those she thinks are beneath the Finches, such as the Cunninghams, and has very racially prejudiced views. She even openly opposes Atticus's decision to defend Robinson, saying that, according to her grandson Francis, Atticus's actions are "ruinin' the family" (Ch. 9). Hence, it can be said that, together, Atticus and Alexandra represent both sides of mankind's dual nature, just like in Poe's short story; Atticus represents the moral conscience, whereas Alexandra represents mankind's evil instinctive nature.