David Koch (net worth: $50.7 billion)

A holder of a bachelor and master degree from MIT, Koch is the executive vice president of Koch Industries, the second-largest closely held company in the U.S. The Wichita, Kansas-based conglomerate operates in oil refining, pipelines, commodities trading, ranching, and paper pulp and had revenue of about $115 billion in 2015. Koch is considered one of the most generous American billionaires, funding many cultural and medical institutions.