In recent years, the EB-5 visa program, which essentially allows wealthy foreigners to buy U.S. citizenship by investing $500,000 in a project that creates U.S. jobs, has exploded: The number of visas granted under the program has more than doubled since 2009. As that has happened, the program has taken on more and more glamorous, big-budget projects and the controversy surrounding it has increased. (Fortune examined the EB-5 program in depth in a recent cover story.)

It would be hard to find a figure who has risen faster in this burgeoning realm than Nicholas Mastroianni, II. In just four years, he has developed a lucrative role raising money for marquee projects such as Atlantic Yards, the giant Brooklyn development anchored by the Barclays Center, home of the NBA’s Nets. Forest City Ratner, which is developing Atlantic Yards, has also retained Mastroianni to raise EB-5 money for its renovation of the Nassau Coliseum, home of the NHL’s Islanders. Other Mastroianni clients include the developers of three large Manhattan projects: the Charles, a 31-story condominium tower on the Upper East Side where the penthouse reportedly sold for $38 million; Bryant Park, a 32-story midtown Manhattan building with a luxury hotel and condos developed by HFZ Capital Group; and 855 Avenue of the Americas, a 41-story mixed-use edifice being developed by the Durst Organization.

All told, Mastroianni’s website boasts of involvement with $5.5 billion in development projects over the years, funded with $1.4 billion in EB-5 money, resulting in “40,000 jobs created.” Those are massive sums given that the entire EB-5 system raised a total of about $1.8 billion last year. Forest City Ratner CEO MaryAnne Gilmartin calls Mastroianni the “ ‘go-to’ leader in the field of EB-5 funding.”

To call Mastroianni’s rise improbable would be an understatement. A squarely built 50-year-old with a Long Island accent, Mastroianni has a long history of legal problems, failed ventures, and unpaid debts—which have continued even as his professional fortunes have turned sharply upward—leaving a legacy of conflicts, judgments, and entanglements.

First, a brief detour: The EB-5 immigration program was created in 1990. Congress allowed the government to sell visas on the grounds that it would direct jobs into needy areas. However, lax federal oversight and aggressive gerrymandering of the special districts required of most EB-5 ventures have allowed developers to use overseas money in ever-wealthier areas, on ever-glitzier projects. The cash is channeled through entities called regional centers—usually private, for-profit businesses—that have been approved by the U.S. Citizenship and Immigration Services, part of the Department of Homeland Security. Regional centers receive administrative fees from the investors and a percentage of what they raise from the developers; on large projects, that can quickly add up to millions.

Big developers have come to love EB-5—once the exclusive province of small ventures that couldn’t get funded anyplace else—because it’s cheap capital, often half the cost of conventional financing. This is because the main lure for most of the immigrant investors (more than 80% of them Chinese) is getting a green card, which is why many are willing to accept little or no return on their $500,000. That allows developers to borrow money at a cost of just 4-6% a year, even when middleman costs are added in.

This is the world in which Mastroianni has thrived, and he certainly has fans. At his request, 17 of his clients, attorneys, and consultants prepared testimonials he submitted to Fortune, vouching for his competence, integrity, charity—even his punctuality.

But Mastroianni’s life and business career have also left a long legal trail. He grew up in Huntington, Long Island, where his father ran the Dover House, a popular restaurant owned by songwriter Burt Bacharach. After two years at Farmingdale State University of New York ending in 1983, Mastroianni moved to Rhode Island, where he went into the construction business at age 19.

Trouble started early. Between 1985 and 1993, court records show, Rhode Island police arrested Mastroianni four times for felony possession of a controlled substance. He pleaded no contest four times, and received a suspended sentence and probation each time. (“It happened,” Mastroianni says through a spokesperson. “It’s the past, life goes on and people move on.”)

Despite the setbacks, Mastroianni began opening businesses at a young age. Recognizing opportunity in a government program that paid for soundproofing homes and businesses near airports, in 1989 he founded a company called Interstate Design & Construction. By underbidding competitors, Mastroianni won dozens of government noise-abatement contracts from Louisiana to Wisconsin to Massachusetts.

But homeowners and subcontractors complained that Interstate did poor work and didn’t complete its jobs, according to newspaper reports dating back to 1996. In May 2000, records show, Mastroianni’s business went into receivership. Banks foreclosed on his office properties and two homes. In 2002, a surety bond company sued Mastroianni to recover costs for completing 28 of his soundproofing jobs and won a $1.1 million default judgment. (Mastroianni didn’t pay until December 2013.)

That wasn’t the end of the troubles. In July 2003, the U.S. Department of Labor sued Mastroianni, accusing him of diverting $401,361 in required employer pension-fund contributions, which were to be made “no less than quarterly.” The suit claimed Mastroianni illegally used the money for “various personal expenses” and to provide seed money for another business that he owned. After the government won a default judgment, the case was finally closed in April 2006 with a negotiated partial restitution; Mastroianni paid $75,000.

Mastroianni had personal financial woes, too. In September 2003, he filed for bankruptcy. In that proceeding, a court-appointed trustee accused him of “knowingly and fraudulently” lying about his assets, including hundreds of thousands in cash and retirement accounts. Ultimately, Mastroianni agreed, “without making any admissions,” that he would not be relieved of his debts in the bankruptcy.

Mastroianni declined to be interviewed for this article but responded in writing through an outside PR consultant to some of the many questions sent to him by Fortune. He blames the receiver who took control of his failing business for not making the required quarterly pension payments. (However, according to government filings, the pension diversion actually began in early 1999, more than a year before a receiver had even been appointed. Rhode Island attorney Allan Shine, who served as the receiver, calls Mastroianni’s claim “ludicrous.”)

In his written comments, Mastroianni insisted that his company successfully completed “numerous projects” but ultimately “outgrew itself.” This period in his career, he added, provided “some valuable lessons on how to build a business.”

Even as legal disputes dragged on in Rhode Island courtrooms, Mastroianni relocated to Palm Beach County, Fla., where he began operating a new company, Allied Capital & Development. Allied specializes in projects “with the highest standards of quality and construction,” according to its promotional materials. Allied’s website says Mastroianni has been “recognized for his commitment to excellence in construction,” and notes that he has “hosted numerous charitable events with both prominent sports figures and political constituents.”

Yet in Florida, virtually every one of the dozen or so projects Allied launched over the past decade has faced delays, lawsuits or construction problems. Allied has completed few of them.

In July 2004, a building collapse at Allied’s townhouse development in Hobe Sound, named “Tranquility,” killed two workers and seriously injured several others. Allied, the developer and construction manager, faced no criminal charges or regulatory penalties, but it settled multiple lawsuits. Afterwards, Mastroianni defended the concrete contractor he’d hired to a local reporter, saying Allied had “checked them out” and had “no reason to believe they caused any problems here.” Local press later reported that the contractor had a history of serious safety violations and lacked workers’ compensation insurance. After investigating the matter, Florida regulators barred the concrete company from doing business in the state and fined it $2.4 million.

Today Mastroianni describes it as “a tragic accident on the part of the General Contractor” and insisted “my partners and I were not constructing the project and had no involvement in the day-to-day operations.” (OSHA’s final report of its investigation, dated Dec. 1, 2004, recounted the role of Mastroianni’s firm in key construction decisions.)

Meanwhile, a lender foreclosed on a nearby Allied townhouse development called Heron Cove after a Mastroianni-led business defaulted on a $12.3-million loan. And four other Mastroianni projects, in Cocoa and Palm Beach County, have not been built. Court records show the developments have faced lawsuits and foreclosure actions. Mastroianni recently settled with one lender who demanded an additional $6.3 million from him and a former partner, who signed personal guarantees.

In numerous instances, Mastroianni has failed even to respond when a lawsuit is filed. For example, in 2007, owners at Marbella Villas, 54 townhouses that Allied developed in North Palm Beach, sued a Mastroianni company, citing its refusal to fix “construction deficiencies and defects,” which homeowners and their lawyers say included a broken water main that allegedly created a sinkhole, unfinished landscaping, a malfunctioning front gate, and structural defects. Mastroianni didn’t contest the charges, and the homeowners won a $1.25 million default judgment. But they have yet to collect a penny. According to the lawyer for the homeowners, by the time the judgment had issued, Mastroianni abandoned the two corporate entities ordered to pay the judgment, allowing their registrations to lapse.

Mastroianni’s refusal to even respond to the complaint is rare for someone who wants to remain in business, says David St. John, whose law firm represented the townhouse owners association. “We’ve done more than a hundred of these cases over the years,” says St. John. “This is one of only two I can remember where the developer just walked. Most of them come to the table and negotiate because they don’t want to ruin their reputation.”

In his responses to Fortune, Mastroianni wrote that the Marbella Villas lawsuit was “a frivolous claim that was filed by an attorney ten years ago in the hopes of leveraging a settlement. All the post-construction complaints, which were normal and customary when building multi-family housing, have been addressed.”

* * *

Mastroianni’s professional fortunes appeared to improve beginning in 2010, when he started using the EB-5 program. He first turned to it to fund his most ambitious development venture: Harbourside Place, a $144-million mixed-use project located on a ten-acre site along the Intracoastal Waterway in the wealthy town of Jupiter, north of Palm Beach.

The project dated back to 2006 and it was going nowhere. Then Mastroianni conceived a plan to finance about $100 million of it with money from wealthy Chinese immigrants. He didn’t just come up with the capital for his own project; he launched a new career as the owner-operator of what became three regional centers, the fund-raising intermediaries that are integral to the EB-5 process.

Mastroianni opened his first EB-5 business, the Florida Regional Center, in 2010 to raise overseas money for Harbourside Place. That project is expected to open in December, two years behind the original schedule. (The city of Jupiter fined Mastroianni’s firm $200,000 this year for missing a completion deadline.) The development includes a 179-room Wyndham Grand hotel, shops, restaurants, office space, an outdoor amphitheater, and a public marina. Golf superstar Tiger Woods, who lives in Jupiter, recently announced plans to open a sports bar in the complex in 2015.

Mastroianni has become a political booster of the EB-5 system. Since 2010, he has donated more than $130,000 to congressional candidates around the country and Democratic party groups. Last year, he retained Washington lobbyists to promote expansion of the EB-5 program. In May, he hired Charles Gargano, a longtime GOP fundraiser whose state and federal appointments have included an ambassadorship to Trinidad and Tobago and a post as New York state’s top economic-development official—exactly the sort of government résumé that appeals to Chinese EB-5 investors. He has also brought in at least one big name for marketing: Mastroianni says he arranged for golf legend Jack Nicklaus to appear at a seminar in China to recruit EB-5 investors for a Florida development where Nicklaus designed the golf course. (Nicklaus’ office didn’t respond to a Fortune inquiry about the appearance.)

Even as Mastroianni has apparently become increasingly prosperous, he continues to be involved in contentious legal battles. Indeed, three of these cases have been filed by attorneys or consultants who used to work for him.

Florida law firm Serber & Associates sued one Mastroianni corporate entity for $80,000 in unpaid fees involving the Jupiter project and won a default judgment in late 2012—only to discover that the entity’s sole asset had been transferred a few months earlier. The firm has now filed a new action to collect the money, claiming a “fraudulent transfer.” Mastroianni declined to comment beyond stating that “we believe our legal position is strong.”

In 2011, Hackley & Robertson, a Palm Beach firm, sued Mastroianni’s Florida Regional Center for unpaid legal fees, eventually winning a $168,454 judgment. In August 2013, Hackley & Robertson filed a “satisfaction of judgment,” acknowledging that a settlement between the parties had been fulfilled. No specifics were given.

Earlier this year, George Ekins, a Los Angeles regional center operator who became Mastroianni’s EB-5 marketing consultant in September 2011, sued three Mastroianni entities, accusing them of paying only a small fraction of the fees they owed, then failing to make good on a 2013 settlement agreement Mastroianni had signed to pay Ekins $900,000. That lawsuit is still pending. (Ekins did not respond to requests for comment.)

Then there was a fourth contretemps with a colleague. Last May, Mastroianni had a brief—but nasty—falling-out with business partner Richard Yellen, a New York real estate lawyer who has worked with him since 2007, both on the Jupiter project and in the EB-5 business. In court papers filed in New York against Mastroianni, the U.S. Immigration Fund (the parent company for Mastroianni’s regional centers), and four other corporate entities, Yellen sought a declaratory judgment confirming his ownership stake and role as co-managing member, and removal of “certain managing members” for “fraudulent and negligent misrepresentations.” If Mastroianni failed to respond to the complaint, Yellen sought an award of up to $20 million for “conversion, self-dealing, unjust enrichment and breach of contract.” Four months later, he withdrew the claim.

“Yeah, that’s a public record,” says Yellen. “Partners who are in business sometimes have disputes.” Yellen remains in business with Mastroianni and calls him “a very talented guy” who “may not be everybody’s cup of tea.” (Mastroianni’s spokesperson relayed a statement that Yellen and Mastroianni “are engaged in discussions to settle their differences.”) Adds Yellen: “Nick comes from a construction background…You know, there’s no question Nick is a tough guy.”

Asked about his pattern of conflict with business associates, Mastroianni responded that upon entering the EB-5 business, “we encountered some individuals who made representations about what they could do to support our effort that turned out not to be the case. We then moved on to identify those experts capable of supporting the EB-5 business.”

After initially failing to respond to Fortune’s requests for information, Mastroianni retained crisis-communications consultant Chris Lehane, an aggressive former Clinton White House strategist who provided two sets of written comments. These were accompanied by 17 testimonial letters that Mastroianni solicited from banks, lawyers, consultants, and clients in his EB-5 business.

Often employing similar language, all offered lavish praise. “In all aspects of our relationships, I have found Nick to be honest, forthright, and punctual,” wrote EB-5 economist Michael Evans. “You will not find a finer person to work with than Nick Mastroianni.”

“I am glad to call Nick a friend,” wrote Andrew Joblon, senior vice president of acquisitions at Fisher Brothers, a prominent New York developer, who noted that Mastroianni had raised $225 million in EB-5 money for two of his company’s Manhattan projects. “He has a great sense of humor, genuine care for others, and love for life.” Forest City Ratner CEO Gilmartin stated that she has “witnessed first-hand his competence and collaborative talents.”

Mastroianni’s package of testimonials included letters from two different executive vice presidents at Signature Bank, which Mastroianni’s company uses to escrow investors’ EB-5 funds. With the exception of a single modifier, both concluded with the exact same sentence: “Nick is a tireless worker, a man of his word, and someone who we look to for guidance in this constantly evolving EB-5 marketplace.”

The collection also included an enthusiastic missive from Michael Villella, finance director for the town of Jupiter, who dealt extensively with Mastroianni on the Harbourside Project. Before writing that letter, however, he offered a more nuanced portrait in an interview with Fortune. Jupiter’s experience with Mastroianni has been “reasonably positive,” Villella says. He credits Mastroianni with completing a complex and difficult-to-finance endeavor. Adds Villella: “Do I think he’s the most forthright guy in the world? No. But did he do a good job here? Yes.”

Villella calls Mastroianni “a challenging individual,” who “can be really difficult to work with.” As Villella puts it, “If he didn’t like the work product he got, he’d say, ‘Hell, I’m not paying you. I know we had a contract, but I think your work stinks! I’m not paying you—I don’t care! Get out of here!’ That’s Nick.”

“I go to church every Sunday thankful that [Harbourside] turned out the way it did,” says Villella. “If you look at his past, you could be any one of those people on that list who were in litigation with him. I’m just glad we’re not.”