Dill Harris is considered a characterization of the author Truman Capote. Harper Lee who wrote, "To Kill a Mockingbird" and Capote were childhood friends. These two remained very good friends as adults. Some critics even suspect that Capote did a little more than "help" Harper Lee with the writing of "To Kill a Mockingbird".

Charles Baker “Dill” Harris in the book and the movie enters Maycomb as an outsider, but quickly establishes his place not only as a resident, but as a voice to be heard among kids and adults. At first glance the odd, the fragile-looking young boy in the film appears to have little or no significance to the world unfolding around him. But then his confident nature and willingness to get involved soon has Dill playing a formative role in all the events taking place in Maycomb.

By the end of the film, Dill is ten years old and his personality has begun to take shape. His personal character has a kind innocence, and he keeps a purity of heart, which his friends find very comforting. This could be a result of Tom Robinson’s trial. Notwithstanding the current events, Dill and his best friend still develop a more grown up perspective that enables them to appreciate human goodness without ignoring human evil.

More Info: en.wikipedia.org