WEST PALM BEACH, Fla. >> Author Daniel Keyes, whose novel “Flowers for Algernon” became a classroom staple that explored the treatment of the mentally disabled and the ethics of manipulating human intelligence, has died, his family said. He was 86.

Keyes died Sunday of complications from pneumonia, said his daughter Leslie Keyes.

First published as a short story in 1959, and later as a novel, “Algernon” is a series of journal entries by a low-IQ laborer named Charlie Gordon who participates in experiments that triple his intelligence just as researchers did with a laboratory mouse named Algernon. As the protagonist reaches the height of his brainpower, the mouse’s progress begins to reverse until he dies, a harbinger of what’s to come for Charlie. The very makeup of the book’s entries follows the ascension and decline of the main character, whose writings are filled with spelling and grammatical errors at the start, then soar to sophistication before regressing.

The short story won a Hugo Award for best short fiction and the novel won a Nebula Award from the Science Fiction and Fantasy Writers of America. The book has sold more than 5 million copies. Actor Cliff Robertson won an Academy Award for best leading actor with his portrayal of the book’s main character in “Charly,” a 1968 movie based on the story.

Keyes was born Aug. 9, 1927, in Brooklyn. He said he always wanted to be a writer but his parents dreamed of him becoming a doctor, and he enrolled in a premedical program at New York University. He wrote in his autobiography, “Algernon, Charlie, And I,” that adopting an unchosen vocation was “driving a wedge between me and the people I love,” feelings that planted the first seeds for his story, in which a major theme is the effect Charlie’s intelligence has on his relationships.

The author eventually became a public school teacher and he said “Algernon” would not have happened without the inspiration of a developmentally disabled boy who approached him and said, “Mr. Keyes, I want to be smart,” he wrote in his autobiography.

Besides his most famous work and the autobiography, Keyes also wrote “The Minds of Billy Milligan,” ”Unveiling Claudia” and several other books. “Algernon,” though to this day part of many schools’ curricula, has also been frequently banned for some of its content, appearing as No. 43 on the American Library Association’s 100 most frequently challenged books of the 1990s.

Leslie Keyes said her father wrote to the very end, using a yellow pad he kept by his bedside. He is survived by another daughter, Hillary Keyes, and a sister, Gail Marcus.

His wife, Aurea Vazquez, died last year.