Which To Kill a Mockingbird character is brought up again in Chapter 26, and why does the character come back in this portion of the book?

In Chapter 26, Harper Lee mentions Arthur "Boo" Radley again for the first time since Tom's trial started because the author is about to join the two storylines of the novel.  The chapter updates where Scout is in her school career, and this is a logical tie back to the first part of the book when Scout is consumed with school issues and Boo Radley (items that had lost her attention during the trial portion of the book).

The trial has ended now, and one of the "mockingbird's" (Tom's) stories is finished. However, the reader still does not know the outcome of the other mockingbird's (Boo's) situation. The author does not simply bring Boo back at this point to finishthe Radley plot; she had, in fact "set him aside" for a while to wait for Scout's maturation.

When the novel opens, Scout is innocent to and ambivalent about the prejudice in her town. She sees Boo Radley only as a curiosity and summer entertainment. As Scout goes through the trial with her father and the rest of the town, she matures and develops a more adult view of the world around her. At the point when the trial is over and Tom has met his unjust fate, Scout is ready socially to view Boo in a different light. She is more sympathetic to those who don't fit into Maycomb's society, and thus, she is prepared for the events which take place at the novel's end--she isfinally able to climb into another's skin and walk around in it.