Confidants of Mr. Emanuel’s said he decided to try his hand at business because he wanted financial security for his family, before eventually returning to public service.

Image Mr. Emanuel, who is set to become White House chief of staff, at a news conference on Monday. Credit... Jim Wilson/The New York Times

“He had a number in his head to make enough for the family,” said Ezekiel J. Emanuel, one of Rahm’s two brothers and a prominent bioethicist at the National Institutes of Health.

It was Morton L. Janklow, the literary agent for several former presidents, who introduced Mr. Emanuel to Mr. Wasserstein. Erskine B. Bowles, the White House chief of staff and a former investment banker, also said he recommended Mr. Emanuel. Mr. Emanuel met in Mr. Wasserstein in his New York office, where they had a wide-ranging discussion about the future of financial regulation, as well as Mr. Emanuel’s plans.

Jeffrey A. Rosen, now deputy chairman of Lazard and a former managing director of Wasserstein Perella’s international practice, said Mr. Emanuel was “both a developed and a raw talent.”

“His years in the White House and what he’d done before that really honed what I’d call deal-making instincts, which could be easily translated into the business arena,” Mr. Rosen said. “Plus, he was someone who was well connected in Chicago and highly respected.”

Mr. Emanuel turned out to be an effective banker, proving a quick study with financial concepts, even as he relied on others in his office for heavy number crunching, former colleagues said. He worked 12-hour days and was known among clients for his relentlessness, constantly on the phone or sending e-mail, and being unafraid to pitch deals. Revenue in Wasserstein’s Chicago office climbed significantly after his arrival.

There is no evidence Mr. Emanuel used his political clout on behalf of his clients, but his connections certainly helped drum up business and contributed to his hiring, former colleagues said. Indeed, a partial list of clients from Mr. Emanuel’s Congressional financial disclosure in 2002 is easily linked up to the various strands of his political career, including his time as a fund-raiser for Mayor Richard M. Daley of Chicago and then for Mr. Clinton’s first presidential run.