Net worth: $41.3 billion
Wealth source: Koch Industries
Residence: Wichita, Kan.
World ranking Tied for 6th
The elder Koch brother is the CEO of Koch industries and, like his brother David, owns a 42 percent share in the company. The siblings have expanded dramatically the business they inherited from their father, Fred. Originally involved mainly in oil refining, Koch Industries is involved in a wide variety of ventures, including pollution control, minerals, and ranching.