Harper Lee modeled many of the characters in To Kill a Mockingbird after people she knew. you will see that Atticus Finch and Harper Lee's father Amasa Coleman Lee are very similar.
Like Atticus, Amasa Lee was also a lawyer. While the two men shared different opinions on some aspects of racial equality, both Atticus and Amasa defended different races in court. In the book To Kill a Mockingbird, Atticus defended Tom Robinson, who was accused of raping a white woman. Amasa defended two black men who were accused of murdering a white store clerk.
Atticus with Tom Robinson
As we know, Atticus finch believes in treating all people the same and always talks about the Golden Rule and walking in other peoples shoes. Although Amasa didn't always share the same beliefs he did write about the horrors of lynching. Also he published positive stories about the counties black community on the front page of the newspaper that he was the editor of before becoming a lawyer. This shows that both men cared about other races.
Amasa Lee was described as "A good honest man, he had a good family". This is very similar to the way Atticus finch was described by the people of Maycomb county. Also Amasa's friend said "Lee was a very quiet spoken man, when he did talk people listened because he had something to say."-George Thomas Jones. This is also similar to the way Jem and Scout thought of Atticus.
Amasa always stressed the importance of education to his children. In to kill a mockingbird, Atticus also told his kids how important school was. We saw this when scout wanted to quit school after her first day, but Atticus wouldn't let her.
Another way that Atticus Finch was modeled after Amasa Lee was that both of these men had children who thought very highly of them. Harper lee idolized her father. Although being a very busy man, Amasa tried to spend as much time as he could with Harper Lee. As a child she used to sit on the balcony and watch her father defend in court. This is very similar to the way that Jem and Scout looked up to Atticus. They always believed everything he had to say and had many of the same morals that Atticus had. Also Jem and Scout were in the balcony watching Atticus defend in the Tom Robinson case.
Harper Lee witnessed her father yelling at members of the ku klux klan when she was a child. seeing her father standing up for people who couldn't stand up for themselves inspired her to add some of the qualities you see in Atticus Finch in To Kill a Mockingbird.
As you can see Atticus Finch was based off of Harper Lees father in many ways.