The Grosvenors, a storied Washington family and heirs to Alexander Graham Bell, will conclude 122 consecutive years of stewardship over the National Geographic Society at the end of the year when Gilbert M. Grosvenor retires as chairman of the board of trustees.

Grosvenor, 79, announced his retirement before a standing-room-only crowd -- fittingly -- in the Grosvenor Auditorium at the Society's headquarters, just a few blocks from the White House.

"It's time to go," said Grosvenor, reached at his farm near Warrenton. "I've done my thing. It's time for other people to have their turn. I don't think it's proper for an institution like the Geographic Society, which is tied to adventure, science and exploration, to have a chairman approaching 80 years of age."

He will be succeeded by Society President John M. Fahey, 58, who has held that position for 14 years.

Timothy T. Kelly, 55, president and chief executive officer of the global media group, will become president of the National Geographic Society, with both appointments effective Jan. 1.

Grosvenor will become chairman emeritus and will continue to serve as chairman of the National Geographic Education Foundation. His daughter, Lexi Grosvenor Eller, a physician, will remain on the board. But Gil Grosvenor's relinquishing of the chairmanship means the family will, for the first time, not be running or participating in editorial units like books, magazines and digital media.

The National Geographic Society has been one of the great family legacies of Washington since its founding in 1888. Quietly run by five generations of the Hubbard-Bell-Grosvenor clan families, the Geographic inhabits a stately headquarters building five blocks from the White House.

Gil Grosvenor, who had been chairman for 23 years, reflected the society's long tradition of gentlemanly explorers and scientists. The Grosvenors were community stalwarts but rarely in an ostentatious way, preferring to let the magazine speak for them. Gil Grosvenor poured much of his energy into geographic education.

In 2004, President George W. Bush awarded Grosvenor the Presidential Medal of Freedom for his stewardship of the family's enterprise and for advancing "the Society's mission of protecting land and wildlife, teaching young people about geography and instilling in readers a respect for other cultures and nations of the world."

Grosvenor is a director or trustee of numerous foundations and corporations, including the Dian Fossey Gorilla Fund International and Marriott Corp. He also served on the board of the former Chevy Chase Bank.

A native Washingtonian and 1954 graduate of Yale University, Grosvenor spent his entire professional career at the National Geographic Society. He joined as a picture editor in 1954, becoming editor in chief of the magazine in 1970 and in 1980 continuing a family tradition by becoming the society's 14th president.

Grosvenor followed four previous generations of the Bell family, which built the society into a pillar of Washington and American culture.

"It was an idea of Alexander Graham Bell to transform what had been a small technical society of geographers into a popular society whose theme is the world and all that is in it," said Kelly. "When he invented the modern version of the National Geographic at the end of the 19th century, he hit upon an enduring idea. Our job is to continuously breathe new life and relevance into that visionary idea of the Society."

National Geographic is best known for its inimitable yellow-bordered magazine, whose dramatic photographs -- thousands were shot for every one that was published -- brought the world's geography to generations of Americans.

From the 1950s through 1980s, National Geographic magazine -- along with Reader's Digest -- topped U.S. magazine circulation. The magazine's English language edition peaked at 10.8 million in 1989. But the media revolution that started in the 1990s with the expansion of cable television and the onset of the Internet created big challenges for Grosvenor.

In a rare moment of turbulence, the Society ousted the magazine's top editor, Wilbur Garrett, in 1990. Published reports at the time said Garrett pushed for more controversial and hard-hitting coverage of world social problems, which apparently conflicted with the Society's historical vision. Grosvenor was said to be proud of carrying on the magazine's tradition of scrupulous objectivity.

Fahey arrived in 1996. He was a graduate of Manhattan College with a master's degree in business administration from the University of Michigan and brought a background in cable television to the Society. He began his career at Time magazine before moving to HBO, where he helped launch Cinemax.

As the first president of National Geographic Ventures, a wholly owned taxable subsidiary of the Society, he started the National Geographic cable channel, inaugurated the company's tour business, launched a Web channel and a school publishing business, and expanded the magazine into other countries and languages.

"Our economics have reoriented themselves toward cable television as the big driver," said Fahey. "The big challenge in front of us is the future digital world that is so ill-defined in terms of economics. Our ability to achieve the opportunities will be only limited by our imagination."

Fahey serves on the board and the executive committee of the Smithsonian National Museum of Natural History and represents the Society on the U.S. National Commission for UNESCO. He is also a member of the boards of directors of Johnson Outdoors Inc. and Exclusive Resorts.

"Digital media represents tremendous opportunities for National Geographic on a worldwide basis and, in many ways, will allow us to get back to our original membership roots," Fahey said.

The new chairman credited the Grosvenor family for guiding the Society for more than a century. And he singled out his predecessor in particular.

"Gil has devoted his entire life to National Geographic," Fahey said. "His great passion is improving the geography literacy of young people in this country. And he has spent the last 20 years aggressively pursuing that goal and making wonderful progress."