Boo Radley is the anonymous gift-giver leaving the Finch children small gifts in the knothole of the oak tree on his property. Scout initially finds a stick of Wrigley's DoubleMint chewing gum in the knothole of the tree and Jem tells her to immediately spit it out when she tells him where she found it. As the story progresses, Jem and Scout end up finding an entire pack of chewing gum, two Indian head coins, a ball of gray twine, two carved soap figures that resemble themselves, a spelling bee medal, and an old watch on a chain with an aluminum knife in the knothole of the oak tree. Boo Radley gives the Finch children the small gifts as a token of his friendship, which reveals that he is a compassionate, benevolent person. Unfortunately, Nathan Radley fills the knothole with cement as an oppressive tactic to prevent his brother from communicating with Jem and Scout. Jem never gets his opportunity to leave Boo a thank you note and is hurt when he discovers that the knothole has been filled with cement.

Boo Radley is the person who has been leaving little gifts for Scout and Jem in the knot of the old tree. Boo Radley has been shut away in his house for a very long time. He does not come out to socialize with people, and he has sort of become the neighborhood bogeyman. Scout and Jem tell imaginative stories about Boo and who he supposedly is and what he supposedly has done. Boo, of course, is nothing like the stories at all, and Scout and Jem will come to realize this by the end of the novel. Boo leaves the gifts in the tree because it is his way of reaching out to Scout and Jem and making friends. It's his way of sharing a little bit of himself with the other two children, so they won't be so frightened of him and his house.