Names of Characters

Firstly, the book was written in the late 1950s, and this helps to explain some of the names. Atticus is uncommon now, but has ancient Greek and Roman origins and there have been several notable people even in fairly recent history with that name. Scout was fairly common as a term of endearment for children up until a few decades ago, although mostly for boys, so applying it to Jean Louise is possibly a play on her being a tomboy. Arthur Radley is portrayed as a scary character, so it's likely "Boo" was invented as his nickname by kids (the word is still used by people attempting to scare others, and has historical connotations of monsters or ghosts).