Facts of Mukesh Ambani

$19.5 billion
Petrochemicals/India
51. Married, three children

Oversees Reliance Industries, India's most valuable company by market cap, despite stock falling 40% in past year. Merging his Reliance Petroleum with flagship Reliance Industries. As part of deal, will exercise right to buy back Chevron's 5% stake in Reliance Petroleum at $1.2 per share--the same price at which he sold it three years ago. Today the stock trades for $1.80 a share. Increased stake in Reliance Industries last October; paid $3.4 billion to convert 120 million preferential warrants into shares. Reliance Petroleum refinery on India's western coast began operating in December despite falling global demand and declining margins. 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. Brothers may be looking to bury hatchet; played joint hosts at mother's recent 75th birthday bash. Has yet to move into his 27-story home that he's building at a reported cost of $1 billion. Ardent fan of Bollywood films. Wife, Nita, oversees school named after his father.

About Lakshmi Mittal

Indian immigrant heads world's largest steel company; ArcelorMittal was formed via hostile takeover three years ago. Stock in company makes up bulk of his fortune; shares at a four-year low, with steel prices down 75% since last summer. Company forced to pay heavy fines after a French antitrust investigation found 10 companies guilty of price-fixing in European steel markets. Arcelor posted $2.6 billion loss in most recent quarter; announced plans to slow acquisitions, cut capital expenditures, pay down debt. Started in family steel business in the 1970s, branched out on his own in 1994. Initially bought up steel mills on the cheap in Eastern Europe. Company bought 19.9% stake in Australia's Macarthur Coal last year. Also owns pieces of Mumbai's Indiabulls Group, London's RAB Capital; owns stake in, sits on board of Goldman Sachs. Holds substantial cash; owns 12-bedroom mansion in London's posh Kensington neighborhood.

Worth : $19.3 billion
Business: Steel/India

Personal: 58. Married, two children

Carlos Slim Helú Facts

$35 billion

Telecom/Mexico
69. Widowed, six children

Economic downturn and plunging peso shaved $25 billion from the fortune of Latin America's richest man. Global recession testing his ability to live up to the principles he sets for his employees: "Maintain austerity in times of fat cows." Son of a Lebanese immigrant bought fixed-line operator Telefonos de Mexico (Telmex) in 1990; now controls 90% of Mexico's telephone landlines. Would be a billionaire based on his dividends alone. Biggest holding: $16 billion stake in America Movil, Latin America's largest mobile phone company, with 173 million customers. America Movil and Telmex reportedly planning to jointly invest $4 billion to bolster telecom infrastructure in Latin America. Buying up cheap media, energy and retail assets. Last year took stakes in New York Times Co., former billionaire Anthony O'Reilly's Independent News & Media and Bronco Drilling; also increased position in Saks. Baseball statistics aficionado, art collector.

Theo Albrecht

$18.8 billion
Supermarkets/Germany
87. Married, two children

Runs discount supermarket group Aldi Nord; firm holding up amid economic downturn. Sales expected to hit $31 billion in 2008. After World War II he and older brother Karl transformed their mother's corner grocery into Aldi. 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 the northern Germany stores and the rest of Europe. Unable to operate Aldi stores in U.S., Theo developed discount food store Trader Joe's; now has more than 320 U.S. stores. Also owns stake in Supervalu. Became a recluse after being kidnapped for 17 days in 1971; said to collect old typewriters, loves golf

Warren Buffett Facts

$37 billion
Investments/U.S.
78. Widowed, remarried; three children

Last year America's most beloved investor was the world's richest man. This year he has to settle for second place after losing $25 billion in 12 months. Shares of Berkshire Hathaway down 45% since last March. Injected billions of dollars into Goldman Sachs, General Electric in exchange for preferred stock last fall; propped up insurance firm Swiss Re in February with $2.6 billion infusion. Admits he made some "dumb" investment mistakes in 2008. Upbeat about America's future: "Our economic system has worked extraordinarily well over time. It has unleashed human potential as no other system has, and it will continue to do so." Scoffs at Wall Street's over-reliance on "history-based" models: "If merely looking up past financial data would tell you what the future holds, the Forbes 400 would consist of librarians." Son of Nebraska politician delivered newspapers as a boy. Filed first tax return at age 13, claiming $35 deduction for bicycle. Studied under value investing guru Benjamin Graham at Columbia. Took over textile firm Berkshire Hathaway 1965. Today holding company invested in insurance (GEICO, General Re), jewelry (Borsheim's), utilities (MidAmerican Energy), food (Dairy Queen, See's Candies). Also has noncontrolling stakes in Anheuser-Busch, Coca-Cola, Wells Fargo