Who are the main characters in To Kill a Mockingbird?

Atticus Finch.

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Actually the book doesn't revolve around 1 person. the story is told through Scout, but the part's of the book center different people. like Tom Robinson, Jem, and Boo
Theoretically it has to be Scout, as the entire book is from her perspective. Although Atticus and Jem file a claim towards being main characters. So all in all, I would say Scout (Jean Louise Finch) is the main character in To Kill A Mockingbird
The main character of To Kill a Mockingbird is Jean Louis who nickname is Scout, she is also the narrator of the story. She is the daughter of Atticus Finch and sister of Jeremy Atticus finch(jem)
Scout and Jem Finch are the kids, and Atticus Finch is their father.

There is also Boo Radley, and the Finch's maid, Calpurnia.
Mainly Scout, but Jem and Atticus are main characters too.