Dori J. Maynard, a journalist who was at the forefront of the campaign to make the American news media a more accurate mirror of American diversity, died on Tuesday at her home in Oakland, Calif. She was 56.

The cause was lung cancer, her mother, Liz Rosen, said.

At her death, Ms. Maynard was the president and chief executive of the Robert C. Maynard Institute for Journalism Education, a nonprofit organization based in Oakland and named for her father, a former editor and publisher of The Oakland Tribune. Mr. Maynard, who died in 1993, was the first black person in the United States to own a general-circulation daily newspaper.

A former newspaper reporter, Ms. Maynard joined the Maynard Institute not long after her father’s death and became its president in 2001.

There, she continued her lifelong interest in exploring the often rocky landscape where race, class, ethnicity and the news media converge. She lectured frequently on the subject and contributed articles to The Huffington Post, American Journalism Review and other publications.

During Ms. Maynard’s tenure, the institute’s purview included professional development, recruitment, a media watchdog program and a news service, America’s Wire, which provides articles on racial inequity and related subjects to newspapers, magazines and websites. To date, the institute has trained more than 5,000 minority journalists and newsroom managers around the country.

Dolores Judith Maynard was born in Manhattan on May 4, 1958; her parents divorced when she was 5. Her father’s second wife, Nancy Hicks Maynard, was one of the first black women to work as a reporter at The New York Times.

With colleagues, Robert and Nancy Maynard founded the Maynard Institute, originally known as the Institute for Journalism Education, in 1977; after Mr. Maynard’s death, it was renamed in his honor.

Dori Maynard earned a bachelor’s degree in American history from Middlebury College in Vermont and was later a reporter at The Bakersfield Californian; The Patriot Ledger, in Quincy, Mass.; and The Detroit Free Press, where her beats included City Hall and the coverage of poverty.

She and Mr. Maynard became the first father-daughter pair to be named Nieman fellows in journalism at Harvard, he in 1966 and she in 1993. Ms. Maynard was also a fellow of the Society of Professional Journalists.

With her father, she was the author of “Letters to My Children” (1995), a collection of his newspaper columns, for which she wrote introductory essays.

Ms. Maynard’s husband, Charles Grant Lewis, whom she married in 2006, died in 2008. Besides her mother, survivors include two brothers, David and Alex Maynard, and a sister, Sara-Ann Rosen. Her stepmother, Nancy Hicks Maynard, died in 2008.

Under Ms. Maynard’s stewardship, the Maynard Institute sought to educate not only aspiring journalists but also the profession of journalism itself, prodding news organizations to cast a wider net when it came to subjects deemed worthy of coverage.

“The conversation that goes on in the newsroom,” Ms. Maynard told NPR in 2005, “determines not only what stories get into the newspaper or onto your television or radio shows, but also determines all the elements that go into those stories.” She added:

“If that conversation is not managed in a way that allows the diversity of opinion that may be in your newsroom to be reflected in your coverage, important elements of those stories are left out, so that they become not only less relevant to communities of color, but they also shortchange the white community, because they are not finding out what’s going on in neighborhoods and communities other than their own.”

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