Boo Radley is a Caster dog and with Macon Ravenwood as his owner. Boo Radley the dog is his own mystery. He appears wolf-like at times, and like a sluggish, grizzled, old mongrel at others. The Sisters even talk about a wolf that Macon's dad had kept around; making it a question as to how old Boo is.

He is Macon's "eyes" often used to look and watch over Lena when Macon can't be with her and it is also shown that Macon can see whatever Boo is seeing. Boo is also revealed to be how Macon has watched over the local residents of Gatlin during his many years as a shut-in, and in result, knowing all of their secrets much to their discomfort. Boo can usually be seen in the background of a scene in a novel of the series; quietly observing whatever commotion is going on or stumbling upon a scene and to be followed by Macon. Boo is very close and protective over Macon. When he had died, Boo is seen following the rest of the family around, "whimpering like a lost pup" until Macon is revived and brought back to the Mortal world again; once again following him around like he usually does.