Although he comes to the fore only at the end, Boo, or Arthur, Radley is an important presence throughout the novel. He is a recluse who lurks on the edge of Maycomb society, but the children are always aware of him. At first he is the object of their childish fears and lurid imaginings, but by the end they come to realise his humanity. He is revealed to be a shy, humble, and also very good-hearted man who has in fact been looking out for the children all the while when they were so frightened of him, culminating in his rescuing them from the clutches of the depraved Bob Ewell. This forms an important part of the plot.
Scout and Jem's attitude to Boo Radley therefore changes and develops throughout the novel as they grow older and gain greater understanding of the world around them. They come to realise that just because he leads such an unconventional lifestyle that does not make him a monster. On the contrary, he is a true gentleman, one of the most decent figures in the novel, far more so than the hypocritical types who make a great show of going to church and doing good while at the same time entertaining the most virulent prejudices against anyone different from themselves (like the missionary circle in chapter featured in chapter 24).
Atticus's injunction to try and understand other people by putting oneself in their place is fully realised by Scout at the end of the novel, when she walks Arthur home:
Atticus was right. One time he said you never really know a man until you stand in his shoes and walk around in them. Just standing on the Radley porch was enough. (Chapter 31)
At this point, standing in front of the once-dreaded Radley place, the imagined haunt of phantoms, Scout comes to see the world entirely from another person's perspective. She is never to see Boo Radley again, but she has learned a most important life-lesson from him.