6. David Koch

• Net Worth: $25 B                                                                 
• Source of Wealth: diversified, inherited and growing
• Citizen: United States
• Age: 73

Along with his brother Charles, he occupies the fifth spot. His net worth stands at Twenty Five billion dollars and this makes him the twelfth richest person in the world along with his brother. Like his brother, he too studied at Massachusetts Institute of technology. Now, he is the executive  Vice President of Koch Industries.