Boo Radley is a badly misunderstood neighbor of the Finches. He is blamed for every unexplained event in Maycomb, from killing cats and poisoning pecans to peeping in windows at night. Jem and Scout eventually learn that he is not a grim reaper, but a kindly, giving man who badly wants to become their friend. Tom Robinson has also been accused of a terrible thing--beating and raping a white woman--of which he is almost certainly innocent. Both Boo and Tom fit several of Harper Lee's primary themes: prejudice and intolerance is one, while another is that concerning the appearance of guilt and innocence, and how things are not always as they first seem.
Bob Ewell is connected in this manner to Tom. Bob is believed by the jury because of the age-old rule that a white man's word trumps that of a black man. Bob and Boo are reflected in another theme, that of courage and cowardice. The secretive, mysterious Boo--believed to be a reclusive coward who only comes out at night--becomes the hero in the end, confronting the real coward, Ewell, when he attempts to harm Jem and Scout. The two seemingly unconnected plots--that of Jem and Scout's interest in Boo in Part One, and the Robinson trial in Part Two--come together on that fateful Halloween night in the final chapters.