Calpurnia from To Kill a Mockingbird shares her name with Julius Caesar's wife (sometimes her name appears as "Calphurnia"). Calpurnia from history was actually Caesar's second wife. He most likely married her because she was the daughter of an influential Roman, and the marriage gave Caesar more power.
While it would not be accurate to compare Atticus to Caesar other than in saying that both were superb, respected leaders and strategists, Calpurnia from the novel does share some similarities with Calpurnia--especially with Shakespare's version of her in Julius Caesar. For example, both women are dependable and loyal partners to the leaders. Atticus trusts Calpurnia to raise his children and to watch over them when he cannot be home. Caesar had wronged his wife repeatedly by being unfaithful, but she still cares about his safety and tries to warn him not to attend the Senate meeting. Similarly, Harper Lee's Calpurnia does share in some of the strange superstitions and traditions of Maycomb even though she is a sensible woman, and Caesar's wife tries to prevent him from going to the Capitol by telling him about a dream she had and reminding him of the soothsayer's warning.
Lee's Calpurnia is, of course, a much stronger and admirable character than Shakespeare's Calpurnia, but nonetheless, both women faithfully support men who hold highly positions in their communities.
In the book "To Kill a Mocking bird" Calpurnia is Atticus' housekeeper. She is a black woman who has strong ties with her church and community. She has always been in the children's lives. She is like a surrogate mother to the children, Jem and Scout. Scout, Atticus' daughter and Calpurnia tend to argue a lot. Scout is more impudent than Jem. After Calpurnia scolds her for making rude statements about Walter Cunningham pouring syrup all of over his food while he is at lunch with the Finches, Scout tries to talk her dad into getting rid of Calpurnia.
Calpurnia guides the children in manners. She also introduces them to the black community. She has a lot of respect for her employer, because of Atticus taking on the job as Tom Robinson's lawyer and also because of Atticus' treatment of people.
In the south at the time of the book, black women often worked as domestic help in white homes. Jobs were scarce and when there were better jobs to be had most whites had he jobs. Women like Calpurnia spent their lives raising and caring for white children and had played a significant role in the growth and development of the children.
Calpurnia was the last wife of Julius Caesar and a noble woman. I do not know if the name was chosen in the book in relation to this or not.