In addition to rejoining the Harvard faculty in 2011, he jumped into a moneymaking spree. His clock was ticking partly because he knew that the Fed chairmanship, to which he has long aspired, was likely to open up in early 2014, when Ben S. Bernanke’s second term will come to an end.

“With Larry, my wife always says that it’s hard to be happy if you want to have the most money because you’ll never have the most money,” said Jeremy I. Bulow, an economics professor at Stanford University who is a friend and co-author of academic papers with Mr. Summers. “He’s kind of been going about his life just on the basis of ‘who knows what’s going to come next?’ and just sort of maximizing his experiences, given the opportunities in front of him.”

The opportunities have been many over the last two years. Mr. Summers, 58, has been employed by the megabank Citigroup and the sprawling hedge fund D. E. Shaw. He works for a firm that advises small banks as well as the exchange company Nasdaq OMX. And he serves on the board of two Silicon Valley start-ups: both financial firms that may pursue initial public offerings in the next year. One of them, Lending Club, offers loans to consumers and small businesses by making arrangements directly with online investors, a new business model that falls into a regulatory gap that consumer advocates say may lead to risky borrowing.

Before his tenure in the Obama administration, Mr. Summers had accumulated personal wealth of at least $7 million; the last two years have most likely added considerably to that. But his money and Wall Street connections put him in an awkward position, partly because the next person to lead the Federal Reserve will oversee the writing of several key new regulations from the Dodd-Frank financial reform bill.