GLOBAL FINANCE

Ngozi Okonjo-Iweala

Managing director // World Bank

DEBT THREAT In little more than two years as finance minister of Nigeria (Africa's most populous country), Ngozi Okonjo-Iweala transformed its finances, established anticorruption efforts within the cabinet, and wiped out its $30 billion in debt with a $12 billion payment funded by soaring oil revenue. Today, as a managing director of the World Bank, she's responsible not only for the rest of Africa but also for Europe and parts of Asia. Her attempts to reform some of the harshest and most dysfunctional economies in the world have won her fans ranging from Tony Blair and Gordon Brown to Bono. —Felix Salmon

ENVIRONMENT

Jeff Immelt

C.E.O. // General Electric

GREEN MONSTER When General Electric announced the debut of its Ecomagination program, skeptics derided it as an empty gesture. Yet the effort has blunted criticism from environmentalists and proved to be an effective business strategy—much as C.E.O. Jeff Immelt promised. Unveiled in mid-2005, the initiative vowed to increase revenue from green products, improve the company's energy efficiency, and decrease greenhouse-gas emissions. So far, so good. G.E. sold $14 billion worth of Ecomagination products in 2007—from low-energy appliances to L.E.D. traffic lights—and reduced emissions by 4 percent. Other big companies have taken notice. Wal-Mart replaced the fluorescent lightbulbs in its refrigerated display cases in about 500 stores with G.E.'s L.E.D.'s, which emit less heat and will reduce Wal-Mart's energy bill by nearly $3 million a year. —J.L.

BIOTECH

James Thomson

Anatomy professor // University of Wisconsin

SKIN GAME First James Thomson created a controversy; then he resolved it. In 1998, Thomson became the first scientist to isolate human stem cells, which can develop into any tissue in the body and thus have tremendous medical potential. Researchers are currently working to figure out how to "instruct" these cells to replace damaged tissues. But the science has been bogged down in controversy, because until recently the cells could be harvested only from embryos. Last fall, Thomson, 49, announced that he had caused a human skin cell to revert to a stem cell that was virtually identical to those found in embryos. The achievement could open the floodgates of investment. How soon might this bear fruit? "In my lifetime," Thomson says. —David Ewing Duncan