Fantasy author Ursula K. Le Guin died in her Portland home Monday. She was 88.

Her son confirmed her death to the New York Times. He did not provide a cause of death but said her health had been suffering for the past several months.

Born Oct. 21, 1929 in Berkeley, Calif., Le Guin was most famous for her “Earthsea” series of novels, which were adapted into a television miniseries as well as an animated film from Goro Miyazaki, son of the legendary Hayao Miyazaki. Le Guin also wrote dozens of novels — including the popular “Left Hand of Darkness” — collections of short stories, books of poetry and children’s stories. Her work was translated into over 40 languages and sold millions of copies across the globe, with some of her more popular titles remaining in print for over 50 years.

Author Neil Gaiman was among those who mourned Le Guin on Twitter.

“I just learned that Ursula K. Le Guin has died,” he wrote. “Her words are always with us. Some of them are written on my soul. I miss her as a glorious funny prickly person, & I miss her as the deepest and smartest of the writers, too. Still honoured I got to do this,” alongside a video of him presenting her with a lifetime achievement award at the 2014 National Book awards.

Stephen King posted a tribute on Twitter, and wrote that she was “not just a science fiction writer,” but a “literary icon.”

Fantasy author Garth Nix wrote, “I just saw the sad news that Ursula K. Le Guin has died. I think I need to stop working, go for a walk with the dog, and give thanks for all her deep thought, wisdom and insight, distilled into so many massively influential books and stories.”

Rick Riordan posted, “Sad news. I dedicated my most recent book to Ursula Le Guin, one of my biggest childhood influences. ‘Rules change in the Reaches.’ Rest in peace, Ms. Le Guin.”

Le Guin is survived by her husband, three children, two brothers, and four grandchildren.