4. Charles Cadogan

• Net Worth: $5.5 B                                                                 
• Source of Wealth: Real state, inherited
• Citizen: United Kingdom
• Age: 76 

Charles Cadogan, head of one of London's richest and best-known real estate dynasties, passed the reigns onto the next generation in 2012. The 8th Earl Cadogan -- or Charles, to his friends -- stepped down as chair of Cadogan Estates, his family's 300-year-old property portfolio, 38 years after taking over its management. His son Edward, Viscount Chelsea, is now running the business. Edward is overseeing the redevelopment of Sloane Street, a popular shopping destination named after an ancestor, with a new piazza of high-end shops.