AUBURN, Ala. — He ended up as the eulogist at Harper Lee’s funeral last year, but the Alabama historian and author Wayne Flynt did not exactly get along with the novelist when they first met in 1983 in the small lake town of Eufaula, Ala.

He asked her to sign his copy of “To Kill a Mockingbird.”

“She said, ‘No, I only sign for children,’” Mr. Flynt said, laughing, in an interview here. “I thought, you are really discourteous. Essentially, you’re just like all the stuff I’ve read about you.”

But over the next 25 years, Mr. Flynt, 76, a professor emeritus of history at Auburn University, said he became close with the famously reclusive Ms. Lee, who would have turned 91 on Friday. His new book, “Mockingbird Songs: My Friendship With Harper Lee,” is based on their relationship, on his takeaways from visits to the nursing home where she lived in her last years and from letters she sent that give a full sense of a personality that was one of the great literary enigmas of the last half-century.

In one, from March 2006, she declared Truman Capote — her childhood friend and literary rival — a liar.