What truths do we learn about Boo Radley in Harper Lee's To Kill a Mockingbird?

In the beginning of Harper Lee's To Kill a Mockingbird, all we learn about Arthur Radley, who the neighborhood children call Boo Radley, comes from "neighborhood legend" and Miss Stephanie Crawford, a "neighborhood scold" and gossip (Ch. 1). We learn that Arthur fell in with a bad crowd of boys during his teenage years and was arrested. While the other boys were sent to the state industrial school to receive "the best secondary education to be had in the state," Mr. Radley felt that Arthur should be put under house arrest instead. From Miss Stephanie Crawford, we learn that when he was 33 years old, while apparently still under house arrest, Arthur drove a pair of scissors into his father's leg. All of these rumors and myths serve to attempt to explain why the neighborhood never sees Arthur Radley. As a result of these rumors and myths, the neighborhood children have come to believe that Arthur is a dangerous madman who poses a threat to their lives.

As the story of the novel unfolds, while we never learn the exact reason as to why Arthur remains in his house, we learn a few very important truths about him. The first very important truth we learn is that Arthur is actually a very caring, benevolent person who has developed a genuine fondness for Scout and Jem through watching them play in the neighborhood from his home. We begin to see him display his benevolent and caring nature through gifts he starts leaving for the children to find in a knothole of an oak tree on his property. The gifts include chewing gum, two polished pennies dated 1906, bars of soap carved to look just like the children, as well as many other treasures. He further shows benevolence by mending the pants Jem rips on the barbed wire fence while the children make their escape while being shot at by Nathan Radley the night they decide to sneak on to the Radleys' property to try and get a look at Arthur through a window. Later that night, when Jem goes back to the fence to retrieve them, he finds his pants lying on the fence, neatly folded and mended.

The greatest act of care and benevolence Arthur accomplishes is rescuing the children from Bob Ewell the night Ewell attacks the children, planning to kill them. That night, Scout sees Arthur for the first and very last time, and through her description of him, we learn what some readers interpret as a new truth about Arthur: that he may be a person with albinism. We can deduce this based on the following details of Scout's description:

His face was as white as his hands, but for a shadow on his jutting chin. . . . and his gray eyes were so colorless I thought he was blind. His hair was dead and thin, almost feathery on top of his head. (Ch. 29)

All of these characteristics match the description of a person with albinism. Due to lack of pigmentation in their eyes, people with albinism have many vision problems, particularly sensitivity to light. Hence, sensitivity to light serves as one possible explanation for as to why Arthur Radley chooses to remain indoors all the time.