Standing on the grand staircase of Lynda and Stewart Resnick’s opulent Beverly Hills mansion at a party last fall — where Diane Keaton, Bob Iger and Brian Grazer were among the luminaries making small talk over crudités and Sazerac cocktails — the author Walter Isaacson took a moment to thank his hosts.

Not only were the Resnicks giving the party to celebrate his new biography of Elon Musk, they had also been major supporters of his former professional home, the Aspen Institute, donating $36 million to the think tank over the years.

Isaacson was not the only one in the room with reason to be grateful to them. Milling about the house, where works by Picasso, Fragonard and Boucher line the walls, were the museum directors Michael Govan of the Los Angeles County Museum of Art (which has received $90 million from the Resnicks) and Ann Philbin of the Hammer ($30 million) as well as Michael Milken, the former junk bond king who later founded a think tank, the Milken Institute ($25 million).

Overall, the Resnicks — whose Wonderful Company business empire includes Pom Wonderful pomegranate juice, Wonderful Pistachios, Fiji Water, Halos mandarins and Teleflora, the flower-delivery service — have donated $1.9 billion of their estimated $13 billion fortune to academic institutions, climate change initiatives, cultural organizations and programs in California’s Central Valley. Their gifts have landed them on the Chronicle of Philanthropy’s annual list of the 50 biggest donors three times.

“You really have to see them as one of the largest proponents of investing in L.A.’s public institutions,” said Mr. Govan, LACMA’s director.

Ms. Resnick, 81, the driving force behind the couple’s charitable efforts, has become particularly focused on giving back in the Central Valley — specifically Lost Hills, where one out of every two households includes an employee of the Wonderful Company.

Over the past decade, the Resnicks have invested about $580 million in Lost Hills and Delano, another Central Valley town, creating charter schools that offer robotics, yoga and mariachi electives; health, wellness and fitness centers; affordable housing; a park; and a new pedestrian bridge across Highway 46.

“It’s the most satisfying of anything I’ve ever done in my life,” Ms. Resnick said in a recent interview at her home. “You meet these young people. You watch them go through school. You see them come back to the valley, which was my dream. Some of them are going into politics. A lot of them have come back to work for us in middle management jobs, not in the fields like their parents.”

But at a moment when philanthropists are increasingly coming under scrutiny — museums have distanced themselves from the Sackler family for its role in the opioid crisis, Warren Kanders stepped down as vice chairman of the Whitney Museum of American Art after protests of his company’s sale of tear gas, and climate activists have protested museum donors and board members — the Resnicks have found that they are no exception.

They have faced scrutiny for their use of one of California’s often scarce resources: water. A 2016 investigation in Mother Jones found that the Resnicks’ agricultural businesses were “thought to consume more of the state’s water than any other family, farm, or company,” and their operations were critiqued the following year in the documentary “Water & Power: A California Heist.”

Last fall, a pair of activists protested the Resnicks at both LACMA, which named its Lynda and Stewart Resnick Exhibition Pavilion in recognition of a $45 million gift, and the Hammer, which named its Lynda and Stewart Resnick Cultural Center in honor of the couple’s $30 million gift. One of the protesters, Yasha Levine, who has been working on a documentary called “Pistachio Wars,” carried a sign that said “Hammer Celebrates Climate Criminals.”

They have brought a lot of improvements, but it’s not all glitter and gold,” Rosanna Esparza, a Kern County activist who has spoken out against the Resnicks for their water usage, said in an interview.

In response to such criticisms, Ms. Resnick said: “We’ve been attacked for water for generations. We’re not taking anyone’s water out of their tap. I don’t have anything to do with the municipal water supplies.”

Gov. Gavin Newsom of California said, despite criticism of their farming practices, and years of lawsuits that have so far failed to upend the water agreements that benefit them, that the Resnicks had simply made the most of a good business deal.

“These are the rules of the road and the rules that we set up, and they play by them,” Mr. Newsom said. “If we’re going to point fingers, we also have to reflect as policymakers about the system we created.”

The Resnicks’ charitable commitments, he added, have been authentic, consistent and impactful. “I know a lot of fancy rich folks,” said Mr. Newsom, to whom the Resnicks have given generously along with other Democratic candidates. “A lot of them dial in their philanthropy. A lot of them are looking for a big name on the building. This is a different thing. They’re the real deal.”

On a recent afternoon in the Central Valley, Naomi Cruz stood in the classroom at Wonderful College Prep Academy where she teaches middle school Spanish, years after graduating from the school herself in 2018. Manpreet Kaur — who won a Wonderful fellowship that helped her pursue a graduate degree — now serves as Wonderful’s program manager for corporate social responsibility and last year was elected to the Bakersfield City Council. Andy Anzaldo, the grandson of an undocumented farmworker, started working in the Wonderful Company’s pistachio plant right out of college and now serves as its chief operating officer for corporate social responsibility.

“One day there will not be a Stewart and Lynda Resnick. So what’s going to happen to this community?” Anzaldo said, adding that the company therefore aims to build a sustainable model that will last “for hundreds of years.”

The Wonderful Company said the impact is measurable, with rates of prediabetes down among Central Valley employees, over 90 percent of Delano students graduating each year and about 70 percent going on to attend a four-year college. (The Resnicks award more than 300 scholarships every year to graduating seniors.)

The environment has also been among the Resnicks’ priorities. In 2019, they gave $750 million to Caltech for research into climate change and sustainability, at the time the second-largest gift to an American university after Michael Bloomberg’s $1.8 billion gift to Johns Hopkins. A new Resnick Sustainability Center is set to open at Caltech next fall.

“If you can’t solve climate change and sustainability, what’s the sense of curing cancer?” Mr. Resnick said. “This is a long-term problem.”

The couple has directed more than $110 million over the past five years to other universities, and are now announcing a $20 million gift to California Polytechnic State University to establish a career services hub for first-generation students.

In Los Angeles, a city without a long tradition of philanthropy, the Resnicks have modeled big-swing giving and have served as a glamorous nexus of Hollywood, art and politics — they are close to Nancy Pelosi, hosted Norman Lear’s 100th birthday party (attended by the likes of Warren Beatty and Jane Fonda) and recently co-hosted a Los Angeles fund-raiser for President Biden with Steven Spielberg, Shonda Rhimes and others.

“The Resnicks set a great example,” said Ms. Philbin of the Hammer, who plans to step down in November. “We had not directly solicited them for our building campaign, but Lynda reached out and offered the largest gift we have ever received.”

And though Mr. Govan worried that, as the economy collapsed in 2008, the Resnicks might renege on their naming gift for LACMA’s new pavilion, which had just started construction, he said Ms. Resnick told him that support was necessary “now more than ever.”

Raised in Philadelphia — where she regularly visited the Philadelphia Museum — and Los Angeles, Ms. Resnick founded her own advertising agency at 19. (She helped Daniel Ellsberg copy the Pentagon Papers on her ad agency’s Xerox machine.)

In the years since, she has applied her market research approach to charitable undertakings like the ones in the Central Valley, where she learned from focus groups and questionnaires that residents were afraid for their children’s futures.

“You can’t come in and build a school and walk away, you can’t come in and build a hospital and walk away,” Ms. Resnick said. “If you’re going to help, you have to go and stay. You’ve got to stay because staying is the most important thing. And so we stayed.”

Over many years of art collecting — Ms. Resnick is a life trustee at LACMA and a trustee emeritus at the Philadelphia Museum of Art — the couple has amassed a trove of paintings, sculptures and decorative arts from the 16th to the 20th centuries. The art fills their offices and their homes in Beverly Hills and Aspen.

Since 1993, they have had their own full-time curator, Bernard Jazzar, who previously worked at the Getty Museum.

Ultimately their artwork will go to public institutions like LACMA, the Metropolitan Museum of Art, the National Gallery and the Philadelphia Museum of Art, Ms. Resnick said. To this end, she has recently permitted museum directors to come through and express their preferences.

“I’m not building my own museum,” she said. “This will all go to museums. I figure you borrow it during your lifetime, and you give it back to the people when you’re done.”