(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.

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