The philanthropist and activist died after a long battle with prostate cancer, which he was diagnosed with nearly three decades ago. Koch is best known for running the multinational corporation Koch Industries alongside his brother, Charles Koch. David stepped down from his role in the business in June 2018, due to his declining health. Charles Koch, via statement Besides Koch Industries, David is also known for setting up a large political network aimed at garnering votes for Republican politicians. The non-profit he co-founded, Americans for Prosperity, has spent over $1 billion on past elections. Their support of affiliations who deny climate change and oppose gun laws often makes them a target of the Democrats. Socially, David's views were more liberal, as he was a supporter of stem cell research, a woman's right to choose and same-sex marriage. Besides political outreach, Koch also made large donations to medical research and towards the Lincoln Center and the Metropolitan Museum of Art.