What is the story behind Arthur "Boo" Radley?

Arthur, who the children call Boo, apparently mixed with "the wrong crowd," a gang of boys who were finally arrested and brought to court after driving an old car through the town square and locking Maycomb's beadle in an outhouse. Though the other boys were sent to industrial school for punishment, and ironically received excellent educations, Arthur Radley's family preferred to keep him hidden inside the home. After fifteen years living at home, the thirty-three-year-old Boo is rumored to have stabbed his father in the leg with a pair of scissors and then quietly continued about his business of cutting out newspaper articles. Refusing to permit his son to be deemed insane or charged with criminal behavior, Mr. Radley allowed Boo to be locked up in the courthouse basement: "the sheriff hadn't the heart to put him in jail alongside Negroes". Boo was eventually brought back to the Radley home. After Mr. Radley's death, his older brother Nathan arrived to continue to watch over Boo and keep him inside and out of sight.

Mr. Radley (Boo and Nathaniel's father) dies and then Boo is brought back to the house and then after that its the end.