For Developer Bruce Ratner, Nets Purchase Aided Atlantic Yards Project Bruce C. Ratner in July at the Barclays Center site. Bruce C. Ratner did not pretend to be much of a basketball fan when he paid $300 million in 2004 for the New Jersey Nets. Before long, the team had the worst record in the National Basketball Association, and he had a reputation as one of the worst owners in professional sports. But he also had the leverage he needed to pull off a real estate megadeal. The purchase was the most glaring demonstration of Mr. Ratner's single-minded dedication to a goal: building a 22-acre, $4.9 billion project in the heart of Brooklyn, the largest development project in the borough's history. Though the Atlantic Yards plan also called for residential towers, a significant portion of which will be subsidized, he sold it to the public as a way to finally bring professional sports back to the borough. So, how did we get here? Mr. Ratner asked last week, almost giddy, at the ribbon cutting of the nation's most expensive basketball arena, the Barclays Center. We first needed to buy a basketball team, and against all odds we did it. That acknowledgment highlights a characteristic that emerged again and again over the past nine years: Mr. Ratner, one of the most prominent and polarizing figures in real-estate-mad New York, may portray himself as a reluctant developer, but he will do what is necessary to get a deal done. "By nature he's a very generous guy," said Stuart Pertz, an architect who worked for Mr. Ratner in the 1980s but opposed his arena project. Once he's in business, he deals with the business at hand. Since the inception of the Atlantic Yards project in 2003, Mr. Ratner, 67, has revised his plans and timelines so often that critics say the whole thing amounts to an enormous bait and switch. He has spent millions lobbying politicians and donating to civic groups to smooth the way. He persisted through lawsuits, protests, financial problems and the chilling doubts of his relatives. His supporters laud his vision, saying it promises local jobs and affordable housing and creates a new center of gravity in Brooklyn. His critics, citing many of the same facts, deride him for overrunning the neighborhood with a Manhattan-size behemoth. On Friday, Mr. Ratner will find some measure of vindication as the glass-and-rusted-steel home of the rechristened Brooklyn Nets - situated at the intersection of Flatbush and Atlantic Avenues - opens with a week of concerts by Jay-Z, whom he recruited to buy a tiny stake in the team. But the project is far from over. Plans call for 15 residential towers over the next 25 years and, possibly, an office building or hotel. Though groundbreaking on the first of those buildings is scheduled for November, already 18 months behind schedule, neighborhood residents grumble that the area is destined to remain a construction zone in perpetuity. At the same time, there are signs that Mr. Ratner, who is considered the city's most significant developer outside Manhattan, may be winding down his career. He sold his 30 percent share of Forest City Ratner Company for $46.3 million and substantial stock in 2006. And for the first time in decades, he has no other major developments in the pipeline. His focus, he said, is completing what will most likely be his most prominent, if not most profitable, project. In a recent interview, Mr. Ratner acknowledged that Atlantic Yards had been "the most difficult, bruising development project I've done, or could even imagine doing." He bristled at the criticism and lamented the damage that critics had inflicted to his reputation, insisting that he had always sought to "make something wonderful and terrific." "We've kept every single promise we've ever made," he said. We've built the arena. They said we'd never build it. And I'm going to build the affordable housing. His neighborhood critics, who say the opening of the arena does not signify the end of their battle against the development, remain as skeptical as ever. "Mr. Ratner portrays himself as a liberal do-gooder type, but this is as phony as the arena's rust," said Candace Carpentor, a spokeswoman for Develop Don't Destroy Brooklyn, one of the groups representing residents of the surrounding neighborhoods.