David Hamilton Koch (/ˈkoʊk/; born May 3, 1940) is an American businessman, philanthropist, political activist and chemical engineer. He joined the family business Koch Industries, a conglomerate that is the second-largest privately held company in the United States, in 1970. He became president of the subsidiary Koch Engineering in 1979, and became a co-owner of Koch Industries, with older brother Charles, in 1983. He is now an executive vice president.Koch is an influential libertarian.