Conservative billionaire David Koch has died at 79, according to sources close to his family. He retired from Koch Industries and has been largely secluded since June 2018, due to “declining health.” Koch Industries is considered one of the country’s leading conservative political powerhouses, even rivaling the influence of the Republican Party itself. It has battled the Trump administration’s tariffs through lobbying groups. Charles Koch wrote to employees last year that his brother would be missed when he retired. “His guidance and loyalty, especially in our most troubled times, has been unwavering,” he said. Koch was thought to have been diagnosed with prostate cancer and was an active board member of the Prostate Cancer Foundation.