Generations of admiring readers knew Harper Lee as the reclusive author of the classic novel “To Kill a Mockingbird.” But a relative few were given a glimpse of another side of Ms. Lee: that of a witty, impish and loyal pen pal.

The cartoonist Berkeley Breathed was one person who shared a correspondence with Ms. Lee. After her death on Friday at the age of 89, Mr. Breathed wrote on Facebook of the letters they had exchanged through the years. Later, he shared with The New York Times four letters he had received from Ms. Lee over 14 years, with the first coming in 1994 and the last arriving in 2008.

The letters detail the author’s quest for privacy, and show how Ms. Lee, who wrote some of the most beloved characters in fiction, became attached to another endearing figure as she aged: Opus, a penguin in Mr. Breathed’s comic strips.

Mr. Breathed, a longtime fan who first wrote to Ms. Lee in 1972, when he was a high school freshman, said the rural backdrop for his Pulitzer Prize-winning cartoon, “Bloom County,” was inspired by sleepy Maycomb, Ala., the setting for “To Kill a Mockingbird,” and that he had written about a dozen strips that made direct reference to the novel.