Nadine Gordimer was first a writer of fiction and a defender of creativity and expression. But as a white South African who hated apartheid’s dehumanization of blacks, she was also a determined political activist in the struggle to end white minority rule in her country.

Gordimer, who won the Nobel Prize for literature in 1991 for novels that explored the complex relationships and human cost of racial conflict in apartheid-era South Africa, died peacefully in her sleep at her home in Johannesburg on Sunday. She was 90 years old. Her son Hugo and daughter Oriane were with her at the time, Gordimer’s family said in a statement Monday.

The author wrote 15 novels as well as several volumes of short stories, non-fiction and other works, and was published in 40 languages around the world, according to the family.

“She cared most deeply about South Africa, its culture, its people, and its ongoing struggle to realize its new democracy,” the family said. Her “proudest days” included winning the Nobel prize and testifying in the 1980s on behalf of a group of anti-apartheid activists who had been accused of treason, they said.

Per Wastberg, an author and member of the Nobel Prize-awarding Swedish Academy, said Gordimer’s descriptions of the different faces of racism told the world about South Africa during apartheid.

“She concentrated on individuals, she portrayed humans of all kinds,” said Wastberg, a close friend. “Many South African authors and artists went into exile, but she felt she had to be a witness to what was going on and also lend her voice to the black, silenced authors.”

Gordimer struggled with arthritis and rheumatism but seemed to be in good spirits when they last spoke three weeks ago, he said.

“Our country has lost an unmatched literary giant whose life’s work was our mirror and an unending quest for humanity,” South Africa’s ruling party, the African National Congress, said in a statement.

Prof. Adam Habib, vice-chancellor and principal of the University of the Witwatersrand in Johannesburg, described Gordimer as a “revered intellect.”

During apartheid, Gordimer praised Nelson Mandela, the prisoner who later became president, and accepted the decision of the main anti-apartheid movement to use violence against South Africa’s white-led government.

“Having lived here for 65 years,” she said, “I am well aware for how long black people refrained from violence. We white people are responsible for it.”

Gordimer grew up in Springs town, the daughter of Jewish immigrants from Britain and Lithuania. She began writing at age 9, and kept writing well into her 80s.

She said her first “adult story,” published in a literary magazine when she was 15, grew out of her reaction as a young child to watching the casual humiliation of blacks. She recalled blacks being barred from touching clothes before buying in shops in her hometown, and police searching the maid’s quarters at the Gordimer home for alcohol, which blacks were not allowed to possess.

That “began to make me think about the way we lived, and why we lived like that, and who were we,” she said in a 2006 interview for the Nobel organization.

In the same interview, she bristled at the suggestion that confronting the human cost of apartheid made her a writer.