When David Fox Jr. moved back to his native Chicago from New York eight years ago to manage the Chicago office of JPMorgan, he became "the firm's primary face in Chicago," he said.

Three years later, New York-based JPMorgan Chase bought Chicago-based Bank One, boosting JPMorgan Chase's Chicago presence from 500 employees to 15,000 employees.

"Chicago was important before. But with the merger, we literally became the biggest office outside of New York City," Fox said.

Chicago became the company's second headquarters because Jamie Dimon, who would become JPMorgan Chase's chairman and chief executive, had retained his Chicago home and was commuting to New York, Fox said.

"With Jamie here, the organization felt much smaller than it had become and made the transition much easier for all of us," said Fox, son of retired Northern Trust Co. Chairman David Fox.

Just as things were settling down last year, Fox's career received another jolt when the market crashed and credit markets froze, creating more urgency for involvement by Fox and JPMorgan.

"Before that, financing would be done by a company's treasurer, but now the CFO and the CEO were deeply involved," Fox said. "The stakes were much higher, and the company's survival could be at stake."

His experiences surviving bank mergers proved valuable in dealing with the aftermath, said Fox, now 50 and vice chairman of JPMorgan Investment Banking, as well as head of its Midwest and Canada investment banking.

"You can't have any knee-jerk reactions or make snap decisions," he said. "You've got to keep your cool to give good advice."