(CNN)Fantasy novelist Ursula K. Le Guin died Monday afternoon in her Portland, Oregon, home, her son Theo Downes-Le Guin said. She was 88.
"It was unexpected at that moment," Downes-Le Guin said. "Her health had not been great."
The acclaimed author penned everything from short stories to children's books, but was best known for her work in the science fiction and fantasy realm.
Le Guin's stories challenged traditional ideas of power, gender and race with stories of young wizards, dragons and outer space.
She is perhaps best known for her Earthsea series, beginning with "A Wizard of Earthsea" in 1968. They are set on the archipelago world of Earthsea, where language is power, and a young wizard learns about morality and consequences.
She won five Hugo awards, science fiction's most prestigious honor, for titles including "The Left Hand of Darkness," set on the planet of Gethen where fixed gender identity doesn't exist; "The Dispossessed," which Le Guin called an "anarchist utopia" novel, and "The Word for World is Forest," where colonists from Earth have enslaved the native planet population.
Le Guin took many standard tropes of the fantasy and sci-fi genres and left them behind or turned them on their heads. Her books avoid simple black-and-white moral victories, and don't draw stark distinctions between good and evil. Her main characters often address conflict not with a big sword battle or fight, but with brains.
The US Library of Congress designated Le Guin a Living Legend in 2000, for her significant contribution to America's cultural heritage.
She had lived in Portland for almost 60 years and had lived in the same house for the past 36 years.
Downes-Le Guin described growing up with a mother with such a rich imagination. "She was an extraordinary conversationalist," he said. "There was never a wasted conversation."
Last year, Houghton Mifflin Harcourt published a book of her essays titled "No Time to Spare: Thinking About What Matters."
She had also written books on poetry and writing that are still unpublished, Downs-Le Guin said.
Neil Gaiman, a seven-time Hugo winner, remembered Le Guin for her wit and brains.
"Her words are always with us. Some of them are written on my soul," he wrote. "I miss her as a glorious funny prickly person, & I miss her as the deepest and smartest of the writers, too."
Writer Shannon Hale lamented Le Guin's death.
"She is a master storytell(er). She is fierce and frighteningly smart and does not tolerate fools. Her EARTHSEA books are a revelation," Hale tweeted.
"Look at the top tier of writers in science fiction and fantasy today ... and you see the unmistakable traces of Le Guin in their work," author John Scalzi wrote in the Los Angeles Times. "Multiple generations of her spiritual children, making the genre more humane and expansive, and better than it would have been without her."
In 2014, LeGuin was awarded the National Book Foundation Medal for Distinguished Contribution to American Letters. In her speech, she decried commercialism in publishing.
"We live in capitalism. Its power seems inescapable," she said. "So did the divine right of kings. Any human power can be resisted and changed by human beings. Resistance and change often begin in art and very often in our art, the art of words."
Le Guin was born Ursula Kroeber in Berkeley, California. Her mother was a writer and anthropologist and her father was an anthropologist. She went to Radcliffe College in Cambridge, Massachusetts, and received a Masters from Columbia University in New York.
In 1953 she married Charles Le Guin, a historian.
Her website says she wrote 20 novels, six collections of poetry and many short stories.