ANSWER:
Throughout the book, there is many different sub plots, themes, and motives, however, overall the To Kill A Mockingbird is centered around the aspect of Discrimination based on Race. One of the main characters and clear protagonist, Atticus Finch, strives to defend a victim of prejudice in court as it's his job as a lawyer, and his own personal worry.
There is no clear antagonist, expect the family who have accused a black man of crime.
