Who sealed up the knothole in the oak tree an why?

In "To Kill a Mockingbird" by Harper Lee, Nathan Radley seals up the knothole in the oak tree. He does this to stop Boo Radley from leaving gifts for Scout and Jem, as he wants to keep his brother isolated and prevent the children from interacting with him. This act symbolizes Nathan's desire to maintain control over Boo's life and further emphasizes the theme of isolation in the novel.