Dill is also a tribute to Harper Lee's childhood (and lifetime) friend, Truman Capote. Dill shares Capote's wild imagination, propensity and talent for telling stories, and somewhat screwed up family situation.
Dill was always one of my favorite characters in the book, and after I saw Capote I liked him even more.
I think Dill contributes to
- the innocence of children and their perceptions of the world. Dill shows particular interest in Boo, and believes the rumors of the town. He isn't really around though when the character of Boo is redeemed in the end.
- the difference between truth and lies. Dill tells stretchers. This shows that Scout and Jem are able to distinguish between the truth and lies which becomes important by the time the trial is underway.
- the ugliness of prejudice: Remember when he gets sick in the courtroom and talks to Mr. Dolpus Raymond? Raymond respects the fact that it makes Dill physically sick to see someone treated the way Tom is treated by Mr. Gilmer.
Dill functions as someone that can be used to bounce off the tales of Boo Radley. The role of Dill was written in by the author with Truman Capote in mind. He had been a childhood friend whose life had been a lot like Dills.
Dill also enables the writer to use his lifestyle to contrast it against the supportive family that Scout and Jem have. They do not have a mother in their life but they have stability. Dill has his mother but she nor his father are stable parents.
In addition, Dill is the inocense of what is going on around him. He sees the cruel way that the people speak to Tom Robinson and he has to leave the courtroom because it makes him cry. He states what the reality should be. They should speak to Tom with some respect.