Mr. Macklowe began envisioning 432 Park in 2006, when he bought the former Drake Hotel. But he loaded the property with debt and was soon facing foreclosure. CIM Group, a private equity firm, eventually stepped in to save him, although he remains a co-developer. More than one-third of the units are now in contract for nearly $1 billion in potential sales, including a $95 million penthouse that could set a price record if it closes.

Seemingly a success, 432 Park has faced its challenges, said Mr. Macklowe recently during an interview at the condominium’s sales office; he was dressed in a tailored navy suit. “It looks easy,” he said, “but that is like seeing Ted Williams or Joe DiMaggio hit a home run and saying it looks easy.”

The sales office, on the 21st floor of the GM Building on Fifth Avenue, sits 100 feet shy of the lowest floors of 432 Park’s condominium residences, giving potential buyers just a hint of the views to come. But the housing of the sales office there was in some ways a curious choice. In 2003, Mr. Macklowe broke a record in buying the GM Building for $1.4 billion, then used it as collateral on that spectacular $7 billion real estate bet that soured; he rents his offices there.

Where Mr. Macklowe is brash — he performed in the Off Broadway show “Old Jews Telling Jokes” and sometimes reverts to a period accent while telling stories — Gary Barnett, the developer of the tower that may eventually eclipse 432 Park for the Western Hemisphere record, is understated.

Mr. Barnett is by some measures the city’s most active developer. Indeed One57, the 90-story, 1,004-foot-tall tower he is building at 157 West 57th Street, was to have taken the hemisphere record until it was supplanted by 432 Park. But he may yet reclaim the title with his planned 227 West 57th. Just west of One57, the tower has enough air rights to rise 1,550 feet; a feature will be the city’s first Nordstrom department store.

Born Gershon Swiatycki on the Lower East Side, Mr. Barnett, an Orthodox Jew who has 10 children, has always been a mercurial character in New York real estate circles. Formerly a diamond trader in Belgium, he rose to prominence in 2005, when he unsuccessfully challenged Bruce Ratner with a rival bid for Atlantic Yards in Brooklyn. A key to his success has been his quiet ability to amass large parcels from individual property owners in prime Manhattan locations. The process can take years, and requires slow and deliberate strategizing. For One57, for example, Mr. Barnett began buying the air rights some 16 years ago.

“Building tall is not about bragging rights,” he said recently, during a conversation in the nondescript conference room of his offices on Third Avenue; he was wearing slacks and a mock turtleneck. “What drives the building is design, the views, the economics.” He built One57 to its full height “because we couldn’t get in all the air rights any other way — once you have it, the ability to build it, I didn’t want to just throw it away.”