The main similarity between Boo Radley and Tom Robinson is the fact that although they both had good intentions and wanted to help others, they were judged harshly and misunderstood by society.
Boo Radley has a bad reputation around town, and is consider something of a villain in the town's stories. The kids make up crazy lies about him, due to a mixture of curiosity and fear. He is painfully shy and occassionally violent, which means he does not interact with the community often. This, in turn, causes people to be even more scared of him.
Tom Robinson has a similarly bad reputation, but for different reasons. He does not have a reputation as a bad individual, but as an individual from a bad class of people, African Americans. He has not committed any bad action, but people judge him harshly and assume he is a criminal due to their racial prejudices.
Both characters strive to do good and help others throughout the book. Tom Robinson tries to stay out of everybody's way, and only gets in trouble because he feels obligated to help Mayella. Boo Radley similarly helps the children many times, most importantly, when he saves their lives. However, both characters are misunderstood and face a life of pain because of the people's prejudice. Both characters could also be considered "mockingbirds," because the only thing they do is sing (try to be good and do good). Their parallel plots are extremely important as they encompass the main themes of the book.
