Mr. Palladino, a private investigator who had worked for Bill Clinton and other famous clients, died four days after he sustained a severe head injury in an attempted robbery, the authorities said.

Jack Palladino, a San Francisco private investigator with a reputation for bare-knuckle tactics who helped Bill Clinton, Harvey Weinstein, R. Kelly and other famous clients face down scandals, died on Monday at San Francisco General Hospital. He was 76.

Mr. Palladino’s death was confirmed by Melvin D. Honowitz, his family’s lawyer. Mr. Palladino was placed on life support after sustaining a severe head injury on Jan. 28 in what the San Francisco district attorney, Chesa Boudin, called “a brutal attack” in the city’s Haight-Ashbury neighborhood. Two people were arrested in the attack and booked at the San Francisco County Jail on charges that include attempted robbery, assault with a deadly weapon and elder abuse.

Mr. Palladino was known for making surreptitious recordings, deploying attractive women or posing as a journalist to extract information and discredit accusers.

During the 1992 presidential campaign, he was hired by the Clinton campaign after Gennifer Flowers released tapes of phone calls with Mr. Clinton to back up her claim that they had had an affair.

Mr. Palladino embarked on a mission, as he put it in a memo, to impugn Ms. Flowers’s “character and veracity until she is destroyed beyond all recognition.”

“Every acquaintance, employer and past lover should be located and interviewed,” Mr. Palladino wrote. “She is now a shining icon — telling lies that so far have proved all benefit and no cost — for any other opportunist who may be considering making Clinton a target.”

In other cases, Mr. Palladino said that he and his wife, Sandra Sutherland, who was also his business partner and survives him, had claimed to be journalists.

“We all much prefer being who we are, but sometimes you use a deception because nothing else will produce the truth,” he told The New York Times in 1999. “You know if you stated honestly to this person that you were a private investigator, they would lie to you.”

Mr. Weinstein, the once-powerful movie mogul who was sentenced last March to 23 years in prison for s*x crimes, had hired Mr. Palladino’s firm to defend him against accusations of s*xual assault, the journalist Ronan Farrow reported in The New Yorker in 2019.

As a part of its work for Weinstein, Mr. Palladino’s firm “created dossiers on both journalists and accusers,” Mr. Farrow reported.

According to The New Yorker, Mr. Palladino also worked for the singer R. Kelly, who was arrested in 2019 on federal child p**nography and obstruction charges.

The New Yorker reported that Mr. Kelly had been sued in 2002 by Charles Freeman, a man from Kansas City who said that Mr. Palladino had hired him to track down any videotapes related to Mr. Kelly that might be “on the streets.”

The San Francisco Chronicle reported that Mr. Palladino had also spent seven years investigating the deaths at Jonestown, Guyana, where more than 900 people died by suicide or were murdered in 1978 at the behest of the cult leader Jim Jones.

Mr. Palladino and Ms. Sutherland worked out of their home, a Victorian house in Haight-Ashbury, The Chronicle reported in 2000.

They charged $300 an hour at the time, according to The Chronicle, and had worked for clients that included the Hell’s Angels, the Black Panthers and the Teamsters, as well as celebrities like Kevin Costner and Don Johnson. Other clients included the musician Courtney Love and the auto executive John DeLorean. In the 1990s Mr. Palladino ran an investigation to protect the credibility of Jeffrey Wigand, a whistle-blower who helped prosecutors in a case against major tobacco companies.

In his work for the Clinton campaign, Mr. Palladino’s staff scoured Arkansas and beyond, collecting disparaging accounts from Ms. Flowers’s ex-boyfriends, employers and others who claimed to know her, accounts that the campaign then disseminated to the news media.

By the time Mr. Clinton finally admitted to “s*xual relations” with Ms. Flowers, years later, Clinton aides had used stories collected by Mr. Palladino to brand her as a “bimbo” and a “pathological liar.”

John Arthur Palladino was born on July 9, 1944. He graduated from Boston Latin School in 1962. He graduated from the University of California, Berkeley, with a degree in political science in 1968, and received his law degree from the university in 1975. Three years later, he was admitted to the California state bar and received his private investigator’s license, records show.

Mr. Palladino had already been recruited to work as a private eye by another well-known San Francisco sleuth, Hal Lipset, who enlisted Mr. Palladino to pose as a fur thief and work undercover in a prison in Queens in 1972 as part of an investigation into drug dealing and prisoner abuse, according to The Chronicle.

Mr. Palladino told The Chronicle that, as a result of his investigation and grand jury testimony, about 23 guards, undersheriffs and others were eventually indicted.

It was “absolutely legal” for private investigators to mislead, Mr. Palladino told The Chronicle, as long as they didn’t present themselves as law enforcement officials or as representatives of the target of an investigation.

However, as an ethical issue, he said it was “more dicey.”

Kim Green, the editor of Pursuit, a trade magazine for private detectives, said Mr. Palladino didn’t evoke feelings of neutrality, “especially in a profession that values privacy and behind-the-scenes maneuvering — some folks in the investigative community can be pretty skeptical of PIs who become celebrities in their own right.”

She added, “Still, there’s no question he made his mark on the field, as part of that tradition of myth-busting Bay Area sleuths who rejected the trench coat stereotype and modernized the profession.”

Despite his reputation for aggressive tactics, Mr. Palladino said that his methods had to be legal and that he most often presented himself, truthfully and simply, as a private investigator.

“I have to be concerned with how it will be perceived by a judge or jury,” Mr. Palladino told The Chronicle in 2000. “If it looks scummy, it may be discounted.”

Christopher Mele and Megan Twohey contributed reporting.