In Harper Lee's To Kill a Mockingbird, the character Calpurnia is the Finches' cook, but she is also treated like a surrogate mother for both Scout and Jem, whose mother died of a heart attack when Scout was just two years old.
Since Calpurnia behaves as a mother figure, she and Scout often have battles because Scout prefers her independence. For example, Scout informs us early on in the very first chapter that Calpurnia was always telling her to get out of the kitchen, making her come home when she didn't want to, and asking her "why [she] couldn't behave as well as Jem when [Calpurnia] knew he was older" (p. 6). Scout further relays, "Our battles were epic and one-sided. Calpurnia always won, mainly because Atticus always took her side" (p. 6).
As the novel progresses, Atticus must spend more and more time away from home, working on the case, leaving Scout and Jem to Calpurnia's care. The more time they spend with her, the more they see her as a vital protector in their lives. Once, she calls the sheriff and Atticus to protect them from a rabid dog. On another occasion, Scout cries on Calpurnia's shoulder after Jem yells at her to start acting like a girl. At another time, she brings them with her to her own African-American church and defends them from racial prejudice. As they walk with her home from church, the more they learn about her background, her education, the African-American culture, and how she avoids looking arrogant by speak "colored-folks talk" at church, even though she is educated enough to speak "white-folks talk" in the Finches' home. Scout learns a valuable lesson from Calpurnia concerning the fact that just because a person knows more doesn't mean the person has to share the knowledge all the time--"it's not ladylike"--and it won't change anything (Ch. 12, p. 127). As Calpurnia phrases it, African Americans need to learn for themselves.