The billionaire is co-owner and an executive vice president of Koch Industries, a conglomerate that is the second-largest privately held company in the U.S. He's worth an estimated $42.9 billion. As top GOP presidential candidates arrived at a hotel here to court the influential donors of the Koch network, Charles Koch called on retreat attendees to unite with him in a campaign against "corporate welfare" and "irresponsible spending" by both political parties.