Lawyer Melvyn I. Weiss, right, pioneered the use of class-action suits against American corporations accused of fraud. (HERMANN J. KNIPPERTZ/ASSOCIATED PRESS)

Melvyn I. Weiss, a lawyer who pioneered the use of class-action lawsuits to target corporate malfeasance, won billions of dollars for investors and negotiated a landmark settlement for survivors of the Holocaust, but who later squandered his reputation in a kickback scandal that landed him in prison, died Feb. 2 at his home in Boca Raton, Fla. He was 82.

The cause was complications of amyotrophic lateral sclerosis, commonly known as Lou Gehrig’s disease, said his son Stephen Weiss, founding partner of the law firm Seeger Weiss.

The grizzled, lightly bearded son of a New York accountant, Mr. Weiss was sometimes labeled “the king of torts,” a reference to a best-selling legal novel by John Grisham and the branch of law that made Mr. Weiss in­cred­ibly wealthy. Earning more than $10 million each year, he flew to meetings in a private jet, threw lavish hula-themed parties for his employees and outfitted his Long Island mansion with a prodigious gambling room and dozens of works by Picasso.

“Am I in it for the money? Yes,” he told the New York Times in 2004. “What I do with the money is my business.”

Mr. Weiss was a major donor to Democratic candidates and causes, and was a longtime supporter of the Israel Policy Forum, a Manhattan-based organization that advocates for a two-state solution in the Middle East. With his wife, he also established a foundation to pay for the loans of New York University Law School students committed to working in the public interest.

To many legal scholars, however, he was known less for the fortune he amassed than for the fierce, four-decade battle he waged against Wall Street fraud and corruption. As founder of New York-based Milberg Weiss, he oversaw what became the world’s largest class-action law firm, leading a team of more than 200 lawyers, accountants and former FBI investigators who went after investment banks and titans of industry with a wolverine ferocity.

Mr. Weiss in 2007. (Damian Dovarganes/AP)

Representing large groups of investors, the firm successfully sued or settled with dozens of companies it accused of fraud, including the tobacco giant Philip Morris, tarnished “junk bond” investment firm Drexel Burnham Lambert, the health-care giant Aetna and the bankrupt energy conglomerate Enron — a case that was led by William Lerach, a colleague and protege of Mr. Weiss who nearly matched his mentor in prominence and panache.

Working pro bono, Mr. Weiss also represented Holocaust survivors and their families in several cases, including a 1998 negotiation with Swiss banks that resulted in $1.25 billion compensation for assets that had been hoarded in the aftermath of World War II.

Mr. Weiss “was a tremendous force for corporate regularity and transparency,” said Arthur R. Miller, an NYU law professor who credited Mr. Weiss’s background in accounting to his proficiency at detecting corporate fraud. “People could justifiably sleep better at night because a lawyer — Mel, and the lawyers who went into securities fraud after him — created a greater reality of deterrence. Companies behaved better because they knew Mel was out there.”

While Mr. Weiss was championed by clients who saw him as a safeguard against boardroom greed and incompetence, he was simultaneously derided by businesses who viewed him as little more than a leech and opportunist, convincing shareholders to finance legal battles that were effectively paid for out of their own pockets.

Critics said his firm merely waited for companies to suffer financial downturns, alleged that the losses were a result of corporate mismanagement and then pressured corporations to settle rather than risk defeat in court. By 2008, when Mr. Weiss pleaded guilty to conspiracy charges in Los Angeles, the Economist reported that he was “the most hated man in the boardrooms of corporate America.”

By Mr. Weiss’s estimation, his firm netted investors more than $20 billion since it was founded in 1965. Federal investigators found that part of its success was because of millions of dollars in kickbacks, which the firm used to secure plaintiffs in about 180 cases over 25 years. Lerach received a two-year sentence for his role in the scheme, and the firm itself — once formally known as Milberg Weiss Bershad & Schulman — agreed to pay $75 million in a settlement.

More than 250 letters of support were sent to the court on behalf of Mr. Weiss, who was disbarred and spent 12 months in prison, four more in a halfway house and paid $10 million in fines and forfeitures. Retiring to Boca Raton, he worked as a mediator and fished for snapper and bonito.

“It was,” Miller said in a phone interview, “a terrible way to end a magnificent career.”

Melvyn Irwin Weiss was born in the Bronx in 1935 and raised in Queens. A grandson of Jewish immigrants from Russia and what was then Austria-Hungary, he began his working life as an assistant to his father, who sent him into the attics of Bronx tailors and kosher butchers to procure misplaced records and receipts.

Mr. Weiss found that recovering dust-covered financial documents didn’t suit him, and after studying accounting at what is now Baruch College in Manhattan, he took up law at NYU. He graduated in 1959 and served in the Army before founding his own firm with lawyer Lawrence Milberg, who died in 1989.

The duo began to thrive after a set of 1966 revisions loosened restrictions on class-action lawsuits, and Mr. Weiss continued to do robust business even after 1995, when a Republican-controlled Congress passed legislation aimed at curtailing the lawsuits.

Survivors include his wife of 60 years, the former Barbara Kaplan of Boca Raton; three children, Gary Weiss of Huntington, N.Y., Stephen Weiss of Manhattan and Leslie Weiss of Melville, N.Y.; a sister; and seven grandchildren.

While Mr. Weiss credited “money” as the driving factor in his career, he seemed to embrace the contradiction at the heart of his work: that he made money primarily by attacking companies’ overzealousness to do the same.

“There is a strain of greed in our culture,” he told Britain’s Observer newspaper in 2003. “I’ve always had a bleeding heart for people who have been wronged.”