Why is Boo Radley a mockingbird?

The town has developed a myth that Boo is an insane monster that wanders around at night peering into people's windows. Throughout the book, he lives with his brother, who is highly controlling. Boo functions as a misunderstood person who is actually the opposite of what people perceive him to be. Like Tom Robinson, Boo Radley functions as a mockingbird-figure. He is mentally fragile and wants to do good for others.