David Kaiser, a scion of the Rockefeller family who steered one of its philanthropies into a pitched confrontation with the company that provided the family’s prodigious wealth, died on Wednesday July 15 2020 at a family home on Mount Desert Island, Maine. He was 50. As president of the Rockefeller Family Fund, and as an official of Just Detention International, a group dedicated to fighting sexual abuse in prisons, Mr. Kaiser pursued twin passions: combating climate change and reforming the criminal justice system. It was all the more unusual for a great-great-grandson of John D. Rockefeller, the founder of Standard Oil, to confront Exxon Mobil, a successor company to the Rockefeller oil monopoly. Mr. Kaiser’s actions, with the support of his family, upended the generally polite world of philanthropy. Exxon Mobil counterattacked, in public statements and court filings, with accusations that the Rockefellers had masterminded a conspiracy against it. The shift began in 2014, when the Rockefeller Brothers Fund, one of the family’s larger philanthropies, announced that it would drop fossil fuels from its portfolio. Then, in 2016, the Rockefeller Family Fund, under Mr. Kaiser’s leadership, announced its own divestment in an even more pointed way, taking aim at what it called Exxon Mobil’s “morally reprehensible conduct.” A large number of cities and counties across the United States, as well as the state of Rhode Island, have also filed lawsuits demanding that fossil fuel companies help pay the costs of dealing with sea-level rise and other effects of a warming planet. David Walter Kaiser was born on July 27, 1969, in Cambridge, Mass., to Neva Rockefeller Goodwin and Walter Kaiser. His mother, who survives him, is a distinguished fellow at Boston University’s Global Development Policy Center. His father, who died in 2016, was a professor of English and comparative literature at Harvard University. In addition to his wife Rosemary Corbett, and his mother, Mr. Kaiser is survived by two daughters and a sister, Miranda Kaiser. Mr. Kaiser graduated from Columbia University in 1991 with a degree in American history. He and Rosemary Corbett met in 2011 through the online dating service OkCupid.