1. Carlos Slim Helu

$53.5 billion
Telecom, Mexico.
Telecom tycoon who pounced on privatization of Mexico’s national telephone company in the 1990s becomes world’s richest person for first time after coming in third place last year. Net worth up $18.5 billion in a year. Recently received regulatory approval to merge his fixed-line assets into American Movil, Latin America’s biggest mobile phone company. More on Carlos Slim Helu & family
2. Bill Gates

$53 billion
Microsoft, U.S.
Software visionary is now the world’s second-richest man. Net worth still up $13 billion in a year as Microsoft shares rose 50% in 12 months, value of investment vehicle Cascade swelled. More than 60% of fortune held outside Microsoft; investments include Four Seasons hotels, Televisa, Auto Nation. Stepped down from day-to-day duties at Microsoft in 2008 to focus on philanthropy. More on William Gates III
3. Warren Buffett

$47 billion
Investments, U.S.
America’s favorite investor up $10 billion in past 12 months on surging Berkshire Hathaway shares; says U.S. has survived economic “Pearl Harbor,” but warns recovery will be slow. Shrewdly invested $5 billion in Goldman Sachs and $3 billion in General Electric amid 2008 market collapse. Recently acquired railroad giant Burlington Northern Santa Fe for $26 billion.
4. Mukesh Ambani

$29 billion
Petrochemicals, oil and gas. India.
Global ambitions: His Reliance Industries, already India’s most valuable company, recently bid $2 billion for 65% stake in troubled Canadian oil sands outfit Value Creations. Firm’s $14.5 billion offer to buy bankrupt petrochemicals maker LyondellBasell was rejected. Since September company has sold Treasury shares worth $2 billion to be used for acquisitions. Late father, Dhirubhai, founded Reliance and built it into a massive conglomerate.