1) Carlos Slim Helu
Net Worth: $53.5 billion
Source: Telecom
Residence: 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.
• 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) Bill Gates
Net Worth: $53 billion
Source: Microsoft
Residence: 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.
• 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
Net Worth: $47 billion
Source: Investments
Residence: 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.
• "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
Net Worth: $29 billion
Source: Petrochemicals, oil and gas
Residence: 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. 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, gas and petrochemicals businesses.
• Still at odds with Anil over gas supply agreement; awaiting Supreme Court's final ruling.
• Owns cricket team Mumbai Indians.
5) Lakshmi Mittal
Net Worth: $28.7 billion
Source: Steel
Residence: India
• London's richest resident oversees ArcelorMittal, world's largest steel maker. Net profits fell 75% in 2009.
• Mittal took 12% pay cut amid slump but improved outlook pushed stock up one-third in past year.
• Looking to expand in his native India; wants to build steel mills in Jharkhad and Orissa but has not received government approval.
• Started in family steel business in India in 1970s; branched out on his own in 1994.
• Initially bought up steel mills on the cheap in Eastern Europe.
• Earned $1.1 billion for selling his interest in a Kazakh refinery in December.
• Sits on the boards of Goldman Sachs, EADS.
• Upped stake in struggling British soccer team QPR in February.
• Funding 400-foot sculpture to be built in London's Olympic Park in time for 2012 Olympics.
• Owns 12-bedroom mansion in London's posh Kensington neighborhood.
• Daughter-in-law Megha recently bought insolvent German fashion house Escada.
6) Lawrence Ellison
Net Worth: $28 billion
Source: Oracle
Residence: U.S.
• Oracle founder's fortune continues to soar; shares up 70% in past 12 months.
• Database giant has bought 57 companies in the past five years.
• Completed $7.4 billion buyout of Sun Microsystems in January; acquired BEA Systems for $8.5 billion in 2008.
• Studied physics at U. of Chicago; didn't graduate.
• Started Oracle 1977; took public a day before Microsoft in 1986.
• Owns 52% stake in business-software company NetSuite; shares worth $480 million.
• Racing junkie owns 453-foot yacht Rising Sun with pal David Geffen. Won America's Cup in February, besting longtime rival billionaire Ernesto Bertarelli.
7) Bernard Arnault
Net Worth: $27.5 billion
Source: Luxury goods
Residence: France
• Bling is back, helping fashion icon grab title of richest European as shares of his luxury goods outfit LVMH--maker of Louis Vuitton, Moet & Chandon--surge 57%.
• LVMH is developing upscale Shanghai commercial property, L'Avenue Shanghai, with Macau billionaire Stanley Ho.
• Renaissance man owns French tour operator Go Voyages, yacht builder Royal Van Lent; has a stake in French retailer Carrefour.
• Built Le Cheval Blanc in ski resort town of Courchevel, France, where he likes to spend New Year's Eve.
• Father, Jean, who died in January, made small fortune in construction; sale of that business later helped fund Arnault's move into real estate and eventually into luxury goods.
• Still a family affair: son Antoine, 32, and daughter Delphine, 34, sit on LVMH's board.
• Wife is a concert pianist; Arnault himself reported to be an excellent piano player.
8) Eike Batista
Net Worth: $27 billion
Source: Mining, oil
Residence: Brazil
• Vowing to become world's richest man--and he may be on his way. This year's biggest gainer added $19.5 billion to his personal balance sheet.
• Son of Brazil's revered former mining minister who presided over mining giant Companhia Vale do Rio Doce got his start in gold trading and mining. Insists Dad didn't help: "All my businesses started from zero. My father was a problem for me because he never let me near Vale."
• Made a pile in resources and other services, but two-thirds of his fortune comes from relatively new source, OGX Petróleo e Gas Participações, the oil-and-gas exploration company he founded in 2007 and took public a year later.
• Police raided his home in 2008, alleging Batista smuggled gold and unfairly influenced the acquisition of a railroad. He denied all wrongdoing, emerged unscathed.
• Onetime champion offshore powerboat racer.
• Formerly married to Playboy cover girl.
• Provided financing to Rio de Janeiro's Olympic committee, helping the city win its bid for 2016 Olympic Games.
9) Amancio Ortega
Net Worth: $25 billion
Source: Fashion retail
Residence: Spain
• Style maven lords over Inditex; fashion firm, which operates under several brand names including Zara, Massimo Dutti and Stradivarius, has 4,500 stores in 73 countries including new spots in Mexico and Syria.
• Set up joint venture with Tata Group subsidiary to enter India in 2010.
• Betting on Florida real estate: bought Coral Gables office tower that is currently home to Bacardi USA.
• Also owns a luxury apartment complex in Miami; properties in Madrid, Paris, London and Lisbon, a horse-jumping circuit, an interest in a soccer league; has investments in gas, tourism and banks.
• Railway worker's son started as a gofer in a shirt store.
• With then-wife Rosalia Mera, also a billionaire, started making dressing gowns and lingerie in living room.
• Shuns neckties and fanfare.
• Daughter Marta works for Inditex; speculation has it she's being groomed to eventually replace her father.
10) Karl Albrecht
Net Worth: $23.5 billion
Source: Supermarkets
Residence: Germany
• Owns discount supermarket giant Aldi Sud, one of Germany's (and Europe's) dominant grocers.
• Has 1,000 stores in U.S. across 29 states.
• Estimated sales: $37 billion.
• Plans to open New York City store this year.
• With younger brother, Theo, transformed mother's corner grocery store into Aldi after World War II. Brothers split ownership in 1961; Karl took the stores in southern Germany, plus the rights to the brand in the U.K., Australia and the U.S. Theo got northern Germany and the rest of Europe.
• Retired from daily operations.
• Fiercely private: little known about him other than that he apparently raises orchids and plays golf.
Read more?