How does Boo Radley develop theme in To Kill A Mockingbird?There is always this kind of character in books who appears rarely but is referred to...

Boo Radley is used to explore many themes, including
the theme that you should treat people with respect rather than intolerance or
prejudice.

Boo Radley is an important character in the
book, although it is true that he does not appear often.  From the beginning of the
book, the child characters are focused on Boo.  This is to frame the story, and let the
reader know that the story of Boo Radley is important.  In the beginning, we are
introduced to prejudice and intolerance in the town of Maycomb through the rumors about
the Radleys.  Boo is regarded as a monster, and the children act out his story in the
yard.  Atticus tries to encourage his children to be respectful to the Radley family and
Boo in particular.

The prejudice and discrimination faced
by Boo foreshadows the larger societal problem of racial prejudice that we see in Tom
Robinson.  With Tom's case, the story moves beyond the childlike innocence of the theme
we saw in Boo and moves to the deeper, darker realm of the deep-set societal prejudice
that Tom faces.  As with Boo, the children learn that someone is not less than a person
just because he is a member of the "other" and a victim of
society.

At the end of the story, the two plot lines
converge.  This is where the theme is solidified.  Ewell, the person who truly is bad,
tries to attack Scout and Boo saves her, killing Ewell.  We learn that Boo is kind,
gentle and shy but also brave enough to leave his isolation to reach out and help
Scout.