Dill and Jem are both very child-like in their actions when the book opens. However, it is clear that Jem realizes that Dill’s quirky behavior, especially the whoppers he tells about his father, really hide a source of pain. Jem and Dill both learn that people are not always what they seem, and they learn the importance of friendship.
Dill is especially interested in the Radley House.
The Radley Place fascinated Dill. In spite of our warnings and explanations it drew him as the moon draws water, but drew him no nearer than the light-pole on the corner, a safe distance from the Radley gate. There he would stand, his arm around the fat pole, staring and wondering. (ch 1)
By the end of Part 1, Dill has become more self-confident. In the beginning, he over-compensates, telling stories about his rich father and introducing himself by saying he can read. Time with the Finches allows him to move beyond himself and be curious about others.
Dill convinces Jem to spy on the Radleys, and later to act out their story.
Dill Harris could tell the biggest ones I ever heard. Among other things, he had been up in a mail plane seventeen times, he had been to Nova Scotia, he had seen an elephant, and his granddaddy was Brigadier General Joe Wheeler and left him his sword. (ch 5)
As the children get older, the stories become more entertainment than self-serving. Jem and Dill begin to hang out more together, leaving the younger Scout to feel left out.
Dill and Jem learn about courage when Jem loses his pants. Dill is a key player in this experiene, even though he is not there will Jem goes to get them.
Although Dill is not there, Jem learns a lot from the experience with Mrs. Dubose and the mad dog. Both incidents teach him the real meaning of courage, building on the lessons he learns with Dill.