As a somewhat sentimental character who represents Harper Lee's childhood friend Truman Capote, Dill plays a couple of roles in the interplay of character with Jem and Scout. For one thing, he provides comic relief from some of the serious issues with which the novel is concerned. For example, the scene in which the children, on the prompting of Dill, try to lure Boo Radley outside with a fishing pole that holds a note is indeed humorous as is the scene in which the ingenious Dill decides that he and Jem should peep into a window of the Radley house in an attempt to see Boo. Of course, this plan fails abyssmally and the children are frightened by Mr. Radley's shotgun blast; then, they are in trouble with Atticus and Aunt Rachel.
In addition to providing comic relief, Dill also acts as a foil to Scout and Jem. While he does not always enter into the learning experiences of the Finch children, his lies and devious ways serve to underscore the importance of integrity to Jem and Scout in a couple of instances. For instance, when Dill steals money from his mother's purse and runs away from home and hides under Scout's bed, Jem demonstrates his maturation as he tells Dill,
"You oughta let your mother know where you are...You oughta let her know you're here...."
He then breaks "the remaining code of [our]childhood" and informs Atticus because he understands what the consequences of Dill's running away are. In other instances, Dill's behavior is also in contrast to the ethics with which the children are instructed by Atticus, and when his behavior causes negative repercussions, Scout and Jem learn valuable lessons. In addition, Dill's life with a negligent mother is also in contrast to the loving family conditions of the Finch children, so they learn to appreciate their father all the more.