Daniel Keyes, the author of Flowers for Algernon, died on Sunday at the age of 86, the New York Times reports.

According to Keyes' daughter Leslie, the cause was complications of pneumonia.

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Keyes originally wrote Flowers for Algernon as a short story, which was published in The Magazine of Fantasy and Science Fiction in 1959. In 1960, it won the Hugo Award for best short fiction.

Six years later, Keyes turned the novella into a novel, which tied for the Nebula Award that year.Flowers for Algernon has since become a staple in high school reading curriculum and was adapted into a film in 1968.