4. Christy Walton & family

• Net Worth: $25.3 B                                                                 
• Source of Wealth: Wal-Mart, inherited
• Citizen: United States
• Age: 58

Christy Walton is the richest woman in the world. She inherited her wealth when husband John Walton, a former Green Beret and Vietnam war medic, died in an airplane crash in 2005. John's side investment in First Solar had boosted Christy's net worth well above the rest of her family, but the stock sank in 2012, narrowing her lead. In recent months, First Solar stock has revived, up 60% since last August and boosting her net worth by $380 million. The bulk of her holdings are in Wal-Mart, the massive retailer founded by her father-in-law Sam Walton and his brother James in 1962. Christy has received nearly $350 million in Wal-Mart dividends after taxes in 2013.