Robert Siegel, the surviving founder of Gwathmey Siegel & Associates Architects, has sold a majority interest in that firm to Gene Kaufman, the designer of dozens of budget hotel properties around Manhattan. Though Gwathmey Siegel, founded in 1968, is by far the better-known firm, it is Kaufman’s investment that is driving the deal. He will serve as chief executive officer of the new Gwathmey Siegel Kaufman & Associates, while continuing to run his 25-year-old firm, Gene Kaufman Architect.

Charles Gwathmey, the son of well-known painters and a famous bon vivant, was beloved by his clients. When I was writing his obituary for The New York Times in 2009, my phone didn’t stop ringing—Steven Spielberg, Ralph Lauren, and Jerry Seinfeld (among others) wanted to tell me how much they loved Charlie, who gave them some of the most luxurious residences in the world without betraying his modernist roots.

Not surprisingly, the firm was less viable after Gwathmey’s death. While Gwathmey had focused on the residential projects, Siegel was more involved in the firm’s public commissions. But the results have been uneven at best. The Sculpture for Living (a curvy apartment tower near the Cooper Union); an addition to Paul Rudolph’s iconic Art & Architecture Building at Yale University; and the new United States Mission to the United Nations, have received scathing criticism. The firm recently signed a contract to design an expansion of the Museum of Contemporary Art in North Miami, sharing a fee (not to exceed $1.15 million) with the Florida firm R.J. Heisenbottle Architects.

Kaufman, for his part, has a thriving firm, but also his share of critics. His hotels, most of them high-rises on the West Side of Manhattan, often seem dismissive of existing urban fabric. He has bragged of his ability to squeeze the maximum number of rooms into narrow mid-block buildings, making it possible for “flags” like Hampton Inn, Fairfield Inn, and Holiday Inn Express to gain toeholds in the lucrative Manhattan market.

But Kaufman has set his sights higher. Among his current projects is the development of an eight-square-mile island in the Yangtze River in Wuhan, China. “It’s a blank slate, which we don’t usually get at home,” he said by phone from Wuhan.

“I’m not Charlie Gwathmey,” Kaufman said.  "Charlie was unique. I can’t do what he did. I have to make my own way.”