(The Wall Street Journal) -- In nearly five years as Merrill Lynch's chief executive, Stanley O'Neal has remade America's No. 1 stock-brokerage firm. He has transformed "Mother Merrill" into a more Darwinian, performance-driven organisation that puts greater emphasis on riskier bets and relies less on just selling stocks.

O'Neal's higher tolerance for risk has come with a low tolerance for mistakes. He has undertaken periodic -- sometimes brutal -- shake-ups of top executives, including one last week.