In Chapter Ten of Harper Lee's novel To Kill a Mockingbird, Jem and Scout learn something new about their father, whose quiet demeanor, relatively-advanced age, and 'failure' to act like other fathers in the community has led Atticus' children to discount him. It is in this chapter that a rabid dog, known as Tim Johnson, wanders into the Finch's neighborhood, causing alarm among some of the residents. The town sheriff, Mr. Heck Tate, arrives to deal with this new threat to public safety, but instead of taking matters into his own hands, urges the modest attorney to assume the role of marksman and shoot the dog:
“Take him, Mr. Finch.” Mr. Tate handed the rifle to Atticus; Jem and I nearly fainted.
“Don’t waste time, Heck,” said Atticus. “Go on.”
“Mr. Finch, this is a one-shot job.”
To Jem and Scout's astonishment, Atticus does indeed fell the dog with one well-placed shot, prompting Miss Maudie Atkinson to exclaim, "I saw that, One-Shot Finch!" Miss Maudie than proceeds to explain her comment to the children, an addendum of sorts to the information she has been providing to Scout and Jem regarding the father they have held in unwarranted low-esteem. In the following passage, Miss Maudie again refers to Atticus with the nick-name she had given him in his earlier life, when he was known as a great marksman:
“Forgot to tell you the other day that besides playing the Jew’s Harp, Atticus Finch was the deadest shot in Maycomb County in his time.”
“Dead shot…” echoed Jem.
“That’s what I said, Jem Finch. Guess you’ll change your tune now. The very idea, didn’t you know his nickname was Ol‘ One-Shot when he was a boy?"
The nickname that Miss Maudie applied to Atticus Finch, then, is "Ol' One-Shot." Atticus had been the best shot in Maycomb, but put down his rifle when he decided that it gave him an unfair advantage over the creatures at whom he had previously pointed it. The revelation that he is a skilled marksman, as noted, forces Scout and Jem to view their father through an entirely new prism.