How a company staved off financial doom.

Over the past year, Merrill Lynch and Lehman Brothers have provided a crash course in how to destroy century-old Wall Street firms. One company's shareholders are walking away with a $50 billion consolation prize in the form of a merger with Bank of America, however, and the other's are getting hosed.

The difference is that Merrill Lynch's CEO, John Thain, played his cards wisely, while Lehman's CEO, Dick Fuld—along with the CEOs of Bear Stearns, Fannie Mae, Freddie Mac, Washington Mutual, and many other financial-services companies—didn't.

Merrill's Thain is a former president of Goldman Sachs and CEO of the New York Stock Exchange. He was brought into Merrill last fall to fix the damage wrought by his predecessor, Stan O'Neal, the man who bears primary responsibility for Merrill's collapse. Thain's decisions can't be evaluated without understanding what he found when he got there, so here's some quick history.

O'Neal took over Merrill in late 2001, a few months before I left (I'd been a tech-stock analyst in the firm's research department since 1999). Merrill had previously been run by a charming bull of a man named David Komansky (think Tony Soprano meets Ralph Kramden), who was the last in a line of CEOs who oversaw a familial culture known as "Mother Merrill."

Merrill's ranks during the Komansky years were as hefty as he was, and O'Neal's first move upon seizing power was to fire about one-third of the firm. He replaced most of Merrill's senior managers with younger, more aggressive executives. He moved away from steady, fee-based businesses in favor of riskier origination and trading. And he took more risk with the firm's capital.

For several years, O'Neal's strategy was phenomenally successful: In rising markets, the firm minted money, and its stock soared to almost $100 a share. When the real-estate market finally broke, however, the subprime-mortgage securities and other products Merrill had been selling began to pile up on its balance sheet. A few quarters later, when the value of these securities had plunged, Merrill was forced to take a massive write-off, and Stan O'Neal was gone.