The elder Mr. Radley is a minor character whose actions have major implications throughout the novel. The unusually cruel punishment he deals out to his son, Arthur, eventually transforms him into the introverted recluse who becomes known as Boo.
Boo's father--and the whole family, for that matter--"kept to themselves, a predilection unforgivable in Maycomb." Although they did not attend church, the Radley's were highly religious and "worshiped at home." Mr. Radley never spoke with his neighbors, and his home had no screen doors (a rarity in Maycomb); even on Sundays, Maycomb's most social day, the "shutters and doors... were closed." When Jem and Scout spoke to him on the streets, "he would cough in reply."
When Boo got into trouble, Mr. Radley bonded him out of jail--"his word was his bond"--rather than allow him to serve his sentence at the industrial school where the rest of his accomplices were sent. Boo was not seen again for more than a decade. When Boo later attacked his father, Mr. Radley would not allow his son to be sent to the asylum, and Boo eventually returned to the confines of his house.
Mr. Radley lived by strict intimidation and, according to Miss Stephanie,
... he was so upright he took the word of God as his only law...
Calpurnia referred to Mr. Radley as
"... the meanest man ever God blew breath into..."
Miss Maudie explained to Scout that Mr. Radley was a primitive Baptist
"... a foot-washing Baptist... (who) believe anything that's pleasure is a sin."