Mr. Ratner said he was seeking both sizzle and “credibility — which we needed badly,” when he first approached several other celebrities in 2003 about helping him acquire the team. Then he was introduced to Mr. Carter by Drew Katz, the son of one of the Nets’ principal owners, after Jason Kidd, then the Nets’ marquee point guard, suggested that Mr. Carter buy the team.
Mr. Carter’s credibility was indisputable: a product of the Marcy Houses, he had an early career as a drug dealer (and kept a “stash spot” two blocks from the arena site, according to one of his songs) before becoming one of the most successful rap artists of all time. He had also shown talent as a businessman, creating his own record label and what soon became a wide range of other business ventures.
Mr. Ratner was wary. He often says he overcame his concerns about Mr. Carter’s more offensive lyrics — celebrating gangster culture and denigrating women — only after learning there were cleaned-up “radio versions” of the songs, too. And Mr. Carter, he said, appeared nervous about having to meet with David Stern, the N.B.A. commissioner, who asked him to discuss his guilty plea to stabbing a record producer in 1999. (Mr. Carter described the incident, for which he received three years’ probation, as a symptom of “the world I lived in once,” Mr. Ratner recalled.)
Mr. Carter’s involvement frustrated opponents of Mr. Ratner’s development plans in Brooklyn who saw the arena and proposed residential and office towers as a subsidized land grab that could ruin the neighborhood. They complained that residents who might have been wary of Mr. Ratner’s promises to create jobs, nonetheless trusted Jay-Z, who invoked his roots and insisted he could never support “anything that’s against the people.”
“Bringing in someone who grew up in public housing, with a rags-to-riches story, who could identify with Brooklyn and African-Americans, that was slick,” said City Councilwoman Letitia James, a critic of the project. Mr. Ratner played down Mr. Carter’s importance in overcoming opposition. “Had Jay-Z not come along,” he said, “we’d still have an arena.”
In the early years, as the Nets made playoff runs, Mr. Carter freely associated himself with the team, attending games and suggesting how to entertain V.I.P.’s in style, said Brett Yormark, chief executive of the Nets. “He and I would talk about how we could use New Jersey as a lab experiment for Brooklyn,” he said.
He also made himself useful to the basketball staff, persuading Shareef Abdur-Rahim of the Portland Trail Blazers to accept a 2005 trade to the Nets (an injury scuttled the deal) and giving Vince Carter a pep talk after he played poorly in two playoff games in 2007 (he responded with 37 points in the next game).
But the rap star pulled back from the Nets as their fortunes faded and they failed to make the playoffs after the 2007-8 season. “He’s very brand-conscious,” a Nets official said.
It was only after the Barclays Center had cleared all hurdles in December 2009 that Mr. Carter unabashedly stepped forward. He courted LeBron James on behalf of the Nets in 2010 and pursued Carmelo Anthony a year later. And when the Nets’ newest star, Deron Williams, needed advice on where to buy a home, Mr. Carter told him to call.
Aaron Goodwin, an agent who has represented many young players who became N.B.A. stars, said Mr. Carter’s involvement had improved the image of the Nets in athletes’ eyes. “They’re going to take the phone call now,” he said. “They’re going to take the flight in. They’re going to listen. In years past, the Nets wouldn’t have gotten that. But now they’re in the game.”
Mr. Yormark said Mr. Carter was not receiving a fee for his advice or any special deals for his businesses. Yet he has attended both quarterly meetings of the arena’s board of directors, sitting to Mr. Ratner’s right, and keeps in frequent touch by phone and e-mail with Mr. Yormark.
During the Nets’ free-agency deal making this summer — obtaining Joe Johnson and re-signing Mr. Williams, among others, in hopes of improving upon their 22-44 record last season — Mr. Yormark received a call from Mr. Carter, who was following the team’s moves on television.
“He said he was watching ESPN,” Mr. Yormark said, “and the size of our logo was too big, because the word Brooklyn was getting cut off on the ticker at the bottom of the screen. He said, ‘Call ESPN and get them to fix it.’ And he was right. And then they fixed it.”
When Mr. Yormark next sat down for a meeting with Mr. Carter, he recalled, the rap star reminded him of this, saying: “Brett, I’m watching. And every detail matters.”