Clearly Frederick Douglass himself is the main character of his own story. His narrative tells of both his life and escape from slavery while making an argument against the institution itself. As the narrator, the story is of his experiences and thus told through his eyes.
Sophia Auld is an important dynamic character in the autobiography. When we first meet her, she is a genuinely nice, caring woman. Originally from the North, Sophia was not raised having slaves around. It is not until she is married that she experiences having power over another person. This power changes her and makes the once kind hearted person become cold and harsh. Through her we see Douglass' argument that slavery can turn even the nicest people into monsters.
Edward Covey is also an important character in the development of Douglass. Covey, a master skilled in a wide range of deceitful means is known for breaking slaves and making them bend to the will of their masters. Covey (or "the snake") illustrates the most evil of slaveholders but also the turning point in Douglass' life. Douglass stands up to Covey and fights back. Covey is the last master to hit Douglass.