Top 5: most rich people in the world — forbes

#1 Carlos Slim Helu & family

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. His construction conglomerate, Impulsora del Desarrollo y el Empleo, builds roads and energy infrastructure. Son of a Lebanese immigrant also owns stakes in financial group Inbursa, Bronco Drilling, Independent News & Media, Saks and New York Times Co. Newspaper outfit's stock popped in early March on talk he might buy a controlling stake; he denies the rumor. Donating $65 million to fund a research project in genomic medicine with American billionaire philanthropist Eli Broad.

#2 William Gates III

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. Bill & Melinda Gates Foundation dedicated to fighting hunger, improving education in America's high schools, developing vaccines against malaria, tuberculosis and AIDS.

#3 Warren Buffett

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. "We've put a lot of money to work during the chaos of the last two years. When it's raining gold, reach for a bucket, not a thimble." Berkshire Hathaway book value was up 19.8% to $21.8 billion in 2009. Son of Nebraska stockbroker met value investor Benjamin Graham while studying economics at Columbia. Took over textile firm Berkshire Hathaway in 1965, used company as a vehicle to invest in insurance (Geico), food (Dairy Queen), utilities (MidAmerican Energy) and recently green tech (electric-car maker BYD).

#4 Mukesh Ambani

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 Creation. 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. After he died, Mukesh and his brother, Anil, ran the family business together for a brief time. But siblings feuded over control; mother eventually brokered split of assets, with Mukesh getting oil and gas and petrochemicals businesses. Still at odds with Anil over gas supply agreement; awaiting Supreme Court's final ruling. Has yet to move out of the family's high-rise, which he shares with his brother, into his new 27-story home in downtown Mumbai. Owns cricket team Mumbai Indians.

#5 Lakshmi Mittal

London's richest resident oversees ArcelorMittal, world's largest steelmaker. Net profits fell 75% in 2009. Mittal took 12% pay cut amid slump but improved outlook pushed stock up a third in past year.