Last year, even when Niederauer was prepared to sell his company to Deutsche Boerse, he insisted that he be chief executive of the combined company. The deal ended up being quashed by German regulators.

But with the agreement by IntercontinentalExchange to buy NYSE Euronext for $8.2 billion, Niederauer has accepted he will have to at the very least play second fiddle. He will become president at the combined company, while still running the New York Stock Exchange, and report to ICE CEO Jeff Sprecher.

"In a sense he must be very frustrated because some of the big things he was trying to do did not work out," said Andre Cappon, president of CBM Group, a New York-based consultant for global exchanges.

To an extent, the world may have left Niederauer behind. His expertise was in stock trading, a business that now has razor-thin margins and is increasingly left to computers.

Sprecher, on the other hand, has ascended as derivatives have become a key part of financial markets and the financial crisis made listed derivatives relatively more important.

Born in Indiana near the Kentucky border, and raised in Madison, Wisconsin, he has a down-to-earth aura that belies his ambitious type-A personality, say people who know him.

Sprecher has not met with constant success, but when something goes wrong, he moves on.

"He's not afraid to fail," said one person who knows Sprecher well.

Among his misses: a failed bid to buy the Chicago Board of Trade in 2007, not to mention a failed joint bid for the NYSE with Nasdaq OMX Group Inc.

He made his move for the CBOT at the annual meeting of the Futures Industry Association, in Boca Raton, Florida, where CME Group officials had expected to deliver a progress report on their planned acquisition of their smaller rival.

Sprecher slipped the formal offer under the hotel doors of CBOT Chairman Charles Carey and CBOT CEO Bernard Dan, at about 6:30 in the morning of the conference's first day.

CME Group later raised its bid for CBOT and clinched the deal in mid-2007 - but Sprecher would still finish the year with two key acquisitions, the New York Board of Trade commodity market and Canada's biggest grains exchange.

This summer both Sprecher and Niederauer bid for the London Metals Exchange and lost. Within four months they were talking to each other about a much larger deal.

LETTING GO OF EGO

There was some bad blood between Sprecher and Niederauer last year, when Sprecher's ICE was part of the group that made an unsolicited bid for NYSE Euronext.

NYSE Euronext was instead focused on a different deal: selling itself to Deutsche Boerse. Sprecher admitted in an interview with Reuters that he tried to wreck the Deutsche deal by "calling out every wart and pimple" on the transaction.

The two men stopped talking for about six weeks.

But after ICE posted good fourth-quarter results in February, Niederauer extended an olive branch with a surprising three-word email to Sprecher: "Hey, great quarter."

"He and I had a preexisting friendship and I wondered if it was going to survive my trouble making," Sprecher told Reuters. Then the email arrived.

"He was very magnanimous and so I knew that he saw through what I was doing and we were still very cordial."

Niederauer took over as NYSE Euronext CEO at the end of 2007, just after his predecessor, John Thain, had completed the landmark deal to buy Franco-Belgian Euronext.

After a 22-year career at Goldman Sachs, mostly in equity trading, and just nine months as head of NYSE's trading operations, he took control just before the 2008 financial crisis triggered a seismic shift in the exchange world, one that seemed ill-suited to his background.

Equity investors, burned by scandals and volatility, were trading less and less; meanwhile new regulations would drive more derivatives onto exchanges like ICE and CME.

The answer, Niederauer thought, lay in Deutsche Boerse. But when regulators nixed the deal in February this year, he quickly laid out a new strategic plan for shareholders: clearing and technology - two areas in which ICE already excelled.

By June, Niederauer was saying it was "make-or-break time" for NYSE's nascent U.S. futures operation, which was clearly failing to thrive in the shadow of established rivals.

In working together at the merged venture, Sprecher and Niederauer may each find a comfortable way to co-exist, each playing to his respective strength, some say. But several people, including a NYSE investor and a board member of a rival exchange, questioned whether the partnership can last.

In an interview, Niederauer said he would remain at least through 2014 as an "important senior member" of Sprecher's management team.

He added: "People get too caught up in titles. Let's just worry about making it work and my guess is that if it's still fun for both of us in 2014, or 2015, or whatever, we will keep doing it."

(Reporting By John McCrank, Jonathan Spicer, Josephine Mason and Jessica Toonkel in New York, and Ann Saphir in Chicago; Writing by Jonathan Leff and Dan Wilchins; Editing by Steve Orlofsky)

• A Permanent Economic Emergency