David Rockefeller, the last surviving grandson of John D. Rockefeller, was laid to rest during the first week of April in Westchester, N.Y., after a private funeral. He was 101. His obituaries extolled his banking career, his global accomplishments and, of course, his wealth. Most likely the last high-profile member of one of America’s most fabled families, the former chairman and chief executive of Chase Manhattan bank exerted influence in the corridors of power around the world.

“David Rockefeller was the last great business/statesman,” said Fraser P. Seitel, Rockefeller’s longtime spokesman. “He was really an ambassador without portfolio.” Author Gary Allen writes in The Rockefeller File that in 1973, “David Rockefeller met with 27 heads of state, including the rulers of Russia and Red China.”

But David Rockefeller’s lasting legacy may well be more about philanthropy than his business and geopolitical exploits. He gave $1.8 billion to charity, according to Seitel, more than any of his brothers—John, Nelson, Winthrop or Laurance.

Some of that philanthropy, however, has fomented a family insurrection and led to a fierce and very public battle with ExxonMobil, the direct descendant of John D. Rockefeller’s Standard Oil Company. At the center of this skirmish are two family charities: the Rockefeller Family Fund, created in 1967 by David and his siblings to encourage their grandchildren to become involved in philanthropy, and the Rockefeller Brothers Fund, created in 1940 by David and his four brothers. The research and reporting financed by these two funds led to groundbreaking reports in 2015 that ExxonMobil knew decades ago, from its own research, of the causal connection between the consumption of fossil fuels and climate change.

“For over a quarter-century, the company tried to deceive policy-makers and the public about the realities of climate change, protecting its profits at the cost of immense damage to life on this planet,” wrote David Kaiser, David Rockefeller’s grandson and president of the Rockefeller Family Fund, in the New York Review of Books in December. “Our criticism carries a certain historical irony. John D. Rockefeller founded Standard Oil, and ExxonMobil is Standard Oil’s largest direct descendant. In a sense, we were turning against the company where most of the Rockefeller family’s wealth was created.”

That irony is further accentuated by the relationship between Chase Manhattan and Exxon. When David ran Chase Manhattan it was known as the “energy bank” and was a major Exxon shareholder. “Any oil company in those days that had financial needs dealt with Chase,” including Exxon, Seitel said. Former Exxon CEOs Lee Raymond and Rex Tillerson, now the U.S. secretary of state, were directors at JP Morgan Chase & Company, originally Chase Manhattan. Conversely, former Chase Manhattan board chairman and CEO Walter Shipley served on ExxonMobil’s board.

Both of the funds, and the Rockefeller family members who serve on their boards, declined comment for this story. But past news reports show David Rockefeller was supportive of their efforts.

“More and more people are recognizing it as one of the serious problems that faces the Earth and that if we don’t deal with it soon it’ll be much worse,” David Rockefeller said about climate change in a 2006 interview with the Chronicle of Philanthropy. At the same time, he announced he would donate another $250 million to the upstart Rockefeller Brothers Fund upon his death, which will make it a $1 billion charity. The timing is significant because his children at the time had already started their campaign to confront Exxon on the climate issue.

The Rockefellers are the 23rd richest family in the U.S., worth a collective $11 billion, spread out among about 200 family heirs, according to Forbes magazine. The streak of activism among some of the Rockefellers comes as no surprise to veteran journalist Michael Gross, who has authored best-selling nonfiction about the family, as well as other ultra-rich Americans.

“Times change, circumstances change, the world changes. Children are not destined to agree with their parents, their grandparents or their great-grandparents. And a group of people who were raised to be intelligent and critical thinkers would be betraying their family if they weren’t,” Gross says. “It’s really astonishing and great and admirable.”

After the news stories about ExxonMobil and its climate-change research broke last year, state attorneys general in New York and Massachusetts began conducting their own fraud investigations, looking into whether ExxonMobil deceived its shareholders by withholding its own research—and thus overstating revenue projections. The SEC also looked at the company.

As it is known to do, ExxonMobil struck back hard, suing the attorneys general of both states in federal court, alleging a “conspiracy” with what it claims are “politically motivated investigations.” Part and parcel of that conspiracy, ExxonMobil claimed, are the two Rockefeller funds, which the oil company sent subpoenaes to demanding documents.

U.S. Rep. Lamar Smith (R., Texas), a noted climate-change denier who chairs the House Committee on Science, Space and Technology, has rallied to ExxonMobil’s defense.

First, he sent a letter to the Rockefeller Family Fund, the Rockefeller Brothers Fund and six other NGOs, as well as all 17 state attorneys general who said they might investigate ExxonMobil. He demanded they all turn over to him all private correspondence among them relating to any potential climate change investigation. The AGs and the NGOs all refused.

In July, Smith subpoenaed the Massachusetts and New York state AGs, charging that the state officials had embarked on an “unprecedented effort against those who have questioned the causes, magnitude or best ways to address climate change.” In February, he issued a second subpoena to the two AGs for documents of their contacts with 25 climate activists, scientists and legal experts. None of them has complied with the subpoenas.

“We believe that the willingness of some members of Congress to echo and defend ExxonMobil’s obfuscation of established climate science is an inexcusable breach of the public trust,” Kaiser wrote in response in the New York Review of Books. “In fact, the Science Committee is doing to the people and organizations it subpoenaed exactly what it accuses us of doing. It is trying to chill the First Amendment rights of those who would petition government, speak freely and freely associate to advocate for responsible climate policies.”

The first volley in this battle between the Rockefellers and ExxonMobil was fired back in 2003 by Neva Goodwin, daughter of David Rockefeller, mother of David Kaiser and co-director of the Global Development and Environment Institute at Tufts University. She co-sponsored a resolution, at Exxon’s annual meeting that year, asking the company to study climate change, unaware at the time it had been quietly doing so for some time. Her resolution failed, but it piqued interest among the family, which formed a committee to delve into the issue.

David Rockefeller even brokered a sit-down with ExxonMobil’s then-CEO Tillerson, the previous CEO Lee Raymond, Goodwin and himself to discuss the family’s climate concerns, Seitel said. Nothing came of the meeting.

In 2008, Goodwin and 15 family members co-sponsored four shareholder resolutions urging key changes at Exxon. Three of them addressed concerns about global warming and renewable energy. The fourth called on the company to name an independent chairman, a plan they said was supported by 73 direct descendants of John D. Rockefeller.

Goodwin pointed out that, at its inception, Standard Oil was the alternative energy of its day: “My great-grandfather saw the need to change from whale oil to petroleum-based fuels,” and Exxon is not showing the “nimbleness and entrepreneurial imagination” to cope with the rapidly changing world, Goodwin said. Her father issued a statement offering his support to the family’s campaign, the Wall Street Journal reported at the time.

Last year, the Rockefeller Family Fund announced it would divest from all fossil fuel holdings, starting with ExxonMobil. Kaiser says a large majority of the family still supports their efforts to fight climate change. But not everyone.

“These family funds do not speak on behalf of all 200 family members,” said Ariana Rockefeller, Kaiser’s cousin, in a CBS interview in December. “I don’t think denouncing a family legacy is the best way to go about doing this.”