IN JUST A

few weeks this summer, a trillion dollars in wealth disappeared from the stock market as the subprime mortgage crisis sent Wall Street's confidence plummeting and made the once-gushing credit markets look like a calcified wasteland. Two Bear Stearns hedge funds evaporated, and the head of the nation's largest mortgage originator, Countrywide's Angelo Mozilo, said home prices were falling "almost like never before."

With easy money up in smoke, it takes a new set of attributes to be truly influential, as we found out preparing this latest installment of our annual list of the 30 most powerful forces in the complex world of business and finance. We're talking about qualities like those held by Russell Read, who's looking for new investments for the nation's largest public pension fund, or Nintendo CEO Satoru Iwata, who zigged when everyone else zagged, making the Wii game console the unexpected star of its industry. And as scrutiny increases in step with the mortgage mess, it's no surprise that regulators and policy makers are in the power spotlight, with some of the harshest glare on Fed Chairman Ben Bernanke.

Ben Bernanke

Chairman, Federal Reserve Board

The hot YouTube clip this summer wasn't footage of the latest celebrity meltdown, but a rant by stock picker Jim Cramer imploring the chairman of the Federal Reserve to cut rates now! Indeed, the spotlight was on Bernanke, 53, as the liquidity that had flooded through the financial markets for the past few years suddenly dried up. The trillion-dollar-plus mortgage market was at a standstill, and even the staying power of Wall Street stalwart Bear Stearns was in question after the collapse of two of its hedge funds. But the mild-mannered Bernanke took the middle road, injecting funds into the financial system before taking steps to cut key interest rates.

Russell Read

Chief Investment Officer, California Public Employees Retirement System

An investment by the nation's biggest public pension fund signals a green light for investors world-wide. And in a year and a half as CIO, Read, 44, has blessed new asset classes for the $240 billion portfolio, including direct investments in infrastructure (think bridges and toll roads) and clean energy, as well as some old ones, like timber and commodities. Why? Read thinks we're returning to an era more like the late 1960s and early '70s, characterized by a massive need for capital in the energy sector and lackluster stock market returns.

John Brennan

Chairman and CEO, Vanguard Group

When Brennan took the reins at Vanguard, it was hard to imagine how he would fill Jack Bogle's sizable shoes. But 10 years later it's clear that Brennan, 53, has put his stamp on the company, which has grown from assets of $200 billion to $1.3 trillion since he took over. Vanguard's late-but-aggressive entry into exchange-traded funds sparked a price war with industry leader Barclays Global Investors. The ETF push also represents Brennan's increased appeal to brokers, who wouldn't touch Vanguard's no-load mutual funds but who can earn commissions on ETF trades. "It won't replace traditional mutual funds, but it's a better way for an adviser to help their client," says Brennan.

Elizabeth Warren

Professor of Law, Harvard University

For years, Warren has been a leading consumer advocate in the financial-services world, pushing for changes in the way lenders relate to customers. Her current targets range from 400% annualized interest rates on overdrafts to credit card agreements so complex it takes a Ph.D. to decipher them. "This is a market that has transformed from being transparent to one loaded with tricks and traps," says Warren, 58. A veteran of the losing battle against the revised bankruptcy law, she's finding a more eager audience in the Democratic Congress.

Steven Nissen

Chairman of Cardiovascular Medicine, Cleveland Clinic

Of all the thorns in the side of big drug companies these days, few are as prickly as Nissen, a 59-year-old cardiologist known for his hard-charging crusade for drug safety. Nissen was the first doctor to sound an alarm about heart risks associated with Merck's Vioxx in 2001. In May he penned a study linking GlaxoSmithKline's diabetes drug Avandia to an increased risk of heart attacks, and Glaxo's stock promptly lost $15 billion in market value. Nissen has consulted with several 2008 presidential candidates, and he's frequently mentioned as a possible Food and Drug Administration chief.

Satoru Iwata

CEO, Nintendo

For a look at the two dozen other members of the Power 30, including Google CEO Eric Schmidt, Blackstone Group CEO Stephen Schwarzman, and investor Warren Buffett, turn to the November issue of SmartMoney Magazine.

In 2002, when Iwata took over, Nintendo was getting crushed by Sony and faced a formidable new foe in Microsoft, with its Xbox console. So Iwata decided to "disrupt" the market, as he put it, by catering to an untapped group: casual gamers. Last year, Nintendo launched the Wii, a console featuring an innovative motion-sensing controller. "It was a risky move," says Michael Cai, an industry analyst with Parks Associates, adding that the Wii could have alienated hard-core gamers while flopping with the casual set. Yet the $250 machine is now outselling Microsoft's Xbox 360 and Sony's PlayStation 3. Iwata, 47, must prove that Wii-mania isn't a fad, but for now his worst problem is that there aren't enough Wiis to go around.

By Ken Bensinger, with Angie C. Marek, Nicole Bullock, Janet Paskin, Anojja Shah, Neil Parmar, Daren Fonda, Dyan Machan and Brad Reagan