Because he hails from Mississippi, Dill Harris is an outsider, but having relatives in Maycomb, as well as being a child, grants him immediate acceptance in the town. Dill is an interesting character because his personality is a compilation of many of the story's other characters. As such, Dill functions as a sort of moral thermometer for the reader in understanding Maycomb. Readers, especially those who don't live in the South, are as much strangers to Maycomb as Dill is, and so he paves the way for the reader's objective observance of the story Scout has to tell.
Dill is an observer much like Scout; however, he has no vested interest or innate understanding of the various folks he encounters. Dill doesn't know his biological father, just as Scout doesn't know her mother. In his attempts to lure Boo Radley outside, Dill's not much different than Bob Ewell with Tom Robinson, although admittedly, Dill's intentions are nowhere near as heinous. He tells enormous lies and concocts unlikely stories just as Mayella does during Tom's trial. He often pretends to be something he isn't, just like Dolphus Raymond does when he comes into town. He risks his safety to run away to Maycomb just as Jem risks his when he goes to collect his pants from the Radleys.
Dill's fantastic stories bring the question of lying to the forefront of To Kill a Mockingbird. Dill's lies incense Scout, but she learns that "one must lie under certain circumstances and at all times when one can't do anything about them," a statement that foreshadows Mayella's predicament. Ironically, Dill, who so easily lies, sobs when the Ewells succeed in the lies they tell about Tom Robinson.