After 21 years as president of the board of the Fine Arts Museums of San Francisco, Dede Wilsey, the socialite and philanthropist whose name became nearly synonymous with museum leadership in the Bay Area, will relinquish her position. At a meeting Tuesday afternoon, the FAMSF board, which oversees two of San Francisco’s largest museums, the de Young and the Legion of Honor, elected Jason Moment as its new head.

At the same time the board appointed Wilsey to the position of chair emerita, an action Wilsey described in a phone interview as an “elevation” to a “more mature title.”

The governance structure of the Fine Arts Museums is complex. Moment will also chair what is called the Corporation of the Fine Arts Museums, with Wilsey as chair emerita of that additional board. The changes are effective immediately with the board vote.

The shift has been long in coming. When The Chronicle reported in July 2016 that the irrepressible — some said autocratic — leader was leaving her position, Wilsey disputed the account and fought back.

“You can’t beat me,” she told the New York Times. The message she would have the paper convey to her detractors was firm: “You will look like a bunch of idiots. And I am going to laugh myself silly.”

She remained as president. On Monday, she said that the spokesman who confirmed the 2016 Chronicle article “was an idiot — he made up that whole story.”

This time, however, it’s for real, as she surrenders a job the board has, even in the face of criticism, repeatedly entrusted to Wilsey without a break over more than two decades. To the last, Wilsey claims to have exercised control over the decision.

“I have been looking for someone younger, who was ready to take over,” she said. “Jason is perfect.”

Moment, 42, has served on the FAMSF board since 2014. A hedge fund manager who also sits on the boards of the UCSF Foundation and Benioff Children’s Hospital, he has chaired the museums’ audit committee for the past three years.

He and his wife, Jessica, are avid collectors of contemporary art, having started with photography and more recently “gravitated toward female artists” including Mary Corse, Helen Frankenthaler and Ellen Gallagher. The couple have two children, a 9-year-old boy and a 6-year-old girl.

“I’m honored and really excited by the job,” Moment told The Chronicle. He would seem a strong choice for an organization that has struggled, at times, to keep its operations in the black — though the organization’s 2018 annual report showed a slight surplus of about $400,000 in an operating budget of $62.5 million. He will also need to repair damage inflicted over several years to the museums’ reputation by the missteps of his predecessor and past boards.

Diane B. Wilsey, known to all as Dede, has long been a fixture in Bay Area social circles. An heir to the Dow chemical fortune, she is the widow of real estate magnate Al Wilsey. Her generosity to the Fine Arts Museums, among many gifts across the region, is legendary. Rare is the major exhibition that does not have her name on the list of top donors, and she famously led the capital campaign that raised $206 million to build the de Young Museum building that opened in 2005.

Yet for years she was said to run the board like a private club, controlling every board appointment and board members’ subsequent decisions. After the death in office of the late director John Buchanan, she took upon herself the role of chief executive officer, generally the director’s job. During that time, there were repeated reports of staff turmoil and high-level resignations, several years of deficits and a wrongful dismissal suit that cost the FAMSF a reported $2 million. Though she was never accused of profiting herself, she appropriated $450,000 without board approval that was eventually repaid by an anonymous donor.

Against that background, Moment would appear to have his hands full.

Moment cited his financial background and different circle of contacts as complementary to the things that, he said, Wilsey provides: generous donations, certainly, but also talents.

“An obvious one is dealing with City Hall,” he said. “None of us want her to step away. She is integral to the museum.”

Thomas P. Campbell, whose appointment as director of the museums was announced in October and whose early performance was lavishly praised by both Wilsey and Moment, echoed the sentiment.

“Dede is so much more than a checkbook,” Campbell said. “She has a steel-trap memory for things that happened decades ago — she’s an institutional memory vault.” He called her “really fun and whip-smart.”

And, crucially, “she can get anyone on the line within minutes.”

For her part, Wilsey says she’s still completely committed to the de Young and the Legion. “I told Tom, ‘The museums have my undying devotion.’ ”

“And then I thought I’d better be careful — I’m worth more to him dead than alive!”