Last fall, senior partners at Kaplan Hecker & Fink, a New York law firm known for championing liberal causes, made a fateful decision: They were going to sideline their hard-charging and crusading founder, Roberta A. Kaplan.

The reign of one of the country’s most prominent lawyers was coming to an end.

Ms. Kaplan was already famous when she founded her law firm in 2017, having won a landmark Supreme Court case that paved the way for marriage equality for gay Americans. The firm soon gained national prominence because of her leadership in the #MeToo movement, and more recently for high-profile victories against white supremacists and former President Donald J. Trump.

But those triumphs couldn’t overcome an uncomfortable reality, according to people familiar with the law firm’s internal dynamics.

In the eyes of many of her colleagues, including the firm’s two other named partners, Ms. Kaplan’s poor treatment of other lawyers — ranging from micromanagement to vulgar insults and humiliating personal attacks — was impairing the boutique firm she had built, the people said. For one thing, they said, she was jeopardizing its ability to recruit and retain valuable employees.

Ms. Kaplan and other partners had also clashed over issues of management and strategy, and some of her colleagues were frustrated by the difficulties of achieving consensus with her, several people said.

Ms. Kaplan was told last fall that it had become untenable for her to remain on the firm’s management committee — a sharp rebuke for a founding partner. She agreed to step down from the committee. The decision began a monthslong chain of events that culminated this week with Ms. Kaplan’s announcement that she was leaving Kaplan Hecker to start a new firm.

The seemingly abrupt departure of a legal star — a gay woman who had become a heroic figure to many on the left for her willingness to take on powerful men like Mr. Trump and Elon Musk — stunned the legal community. But it had been years in the making, according to interviews with more than 30 current and former colleagues, clients and others.

Ms. Kaplan has tirelessly constructed a brand as the go-to lawyer for virtually every liberal cause. This year alone, she won an $83 million jury verdict against Mr. Trump for his having defamed the writer E. Jean Carroll; successfully defended researchers sued by Mr. Musk’s X Corporation; secured a settlement for people challenging the Florida law that critics nicknamed “Don’t Say Gay”; and represented President Biden’s daughter Ashley in a criminal investigation into who stole her diary.

Many former employees said they were proud of the work they had done and admired Ms. Kaplan’s fearless pursuit of big targets. But they also said the workplace environment she had presided over could be unbearable.

This went beyond normal gripes about tough bosses. Ms. Kaplan’s behavior was at times such an issue that a top lawyer at another firm who was her co-counsel in a case reprimanded her over her conduct, and a progressive legal coalition nixed her from a list of candidates for federal judgeships because of her reputation for mistreating employees, according to lawyers familiar with both episodes.

Ms. Kaplan is hardly the only high-powered attorney with a reputation for being a difficult boss. Plenty of male lawyers have engaged in comparable behavior and gotten away with it.

But Kaplan Hecker & Fink was founded on the premise that it would be a “values-driven” law firm free of the macho nastiness that historically characterized many of the country’s elite firms. Ms. Kaplan has said she created it “on the principle that there always must be someone to stand up to a bully.”

Ms. Kaplan, 57, declined interview requests. In a statement to The New York Times hours before she announced her departure on Wednesday, she trumpeted her work against “some of the world’s biggest bullies” but acknowledged that “there are people who don’t like me, which comes with the territory, particularly when you are a woman.”

In response to questions about her workplace demeanor, the firm’s lawyers, Christopher J. Clark and Virginia F. Tent, accused The Times of trafficking in “the hackneyed trope of the powerful professional woman as shrewish, abrasive and vindictive.” They noted that in internal reviews, her colleagues “described Ms. Kaplan as fostering a sense of support and transparency and making her colleagues feel heard and supported in her teams, in addition to being warm, thoughtful and empathetic.”

They added that “Ms. Kaplan’s presence and work at the firm was a significant driver of the firm’s recruitment of legal talent.”

Sean Hecker and Julie Fink, the two top partners remaining at the firm, said in a statement that “Robbie has made immeasurable contributions to the firm, we continue to have mutual respect for her, and we look forward to continuing to collaborate with her.”

While Ms. Kaplan’s new and old firms say they plan to have a cooperative relationship, they are already vying for clients and personnel — and to control the narrative about her exit.

Some of Ms. Kaplan’s defenders believe that her old colleagues are leaking damaging information about her in order to undercut her new firm before it is even off the ground. Her detractors say the legal world should know about her behavior.

Jostling to Join

Growing up outside Cleveland, Ms. Kaplan had mapped out her future by age 12: an Ivy League college, followed by a Manhattan law school, culminating in a job at a prestigious law firm where she would “finally get to fulfill my dream of litigating high-profile, cutting-edge commercial cases,” as Ms. Kaplan put it in her 2015 memoir. (“Yes,” she added, “that was actually my dream.”)

Sure enough, Ms. Kaplan graduated from Harvard and then Columbia Law School. At 31, she made partner at Paul Weiss, where she represented clients like JPMorgan Chase and T-Mobile.

Like many other ambitious young corporate lawyers, Ms. Kaplan was relentless in her pursuit of success — so much so that her future wife, Rachel Lavine, a Democratic operative, once offended her on an early date by comparing her to a Bolshevik willing to spill blood for the sake of victory.

Ms. Lavine began pushing her toward political advocacy, according to Ms. Kaplan’s memoir, “Then Comes Marriage.” In 2013, she won a landmark lawsuit that she had brought on behalf of a lesbian who didn’t want to pay taxes on her dead partner’s estate. The Supreme Court used the case to strike down a key provision of the Defense of Marriage Act, paving the way for the nationwide right to same-sex marriage.

Ms. Kaplan was no longer content just litigating commercial cases. When a hoped-for job in a hoped-for Hillary Clinton administration didn’t pan out, Ms. Kaplan seized the anti-Trump moment and created her own law firm: Kaplan & Company.

Ms. Kaplan’s timing was impeccable. She pitched her firm as a progressive bastion that would combine trailblazing public interest practice with civil and criminal litigation. The goal was to win big rewards for worthy causes while also making its lawyers rich. The cherry on top: The firm was run by a legal giant in a field largely bereft of female leaders, much less gay women.

Liberal lawyers jostled to join.

The firm’s start-up nature made it less bureaucratic, and employees from that time said Ms. Kaplan could be generous and fun to work for. If she liked you, she might share juicy gossip from her social circle, invite you to Shabbat dinner or help you land a judicial clerkship.

The clients — and the billable hours — flowed in. There were headline-grabbing public interest cases, like an ambitious federal lawsuit against the white supremacists and others behind the infamous “Unite the Right” rally in Charlottesville, Va., in 2017. And there were marquee corporate clients like Uber, Airbnb and Pfizer.

Before long Ms. Kaplan added Mr. Hecker, a white-collar criminal defense lawyer, to the name of the firm, along with her co-founding partner, Ms. Fink.

Soon they set up shop high in the Empire State Building. Ms. Kaplan decorated her office with photos of her posing with former President Barack Obama and the Clintons and named a conference room after Ruth Bader Ginsburg.

The Meatball Incident

From the start, Ms. Kaplan’s behavior alienated some of her new hires.

“Robbie was a screamer, she yelled a lot, and that was not an experience I had before,” said Christopher Greene, who had joined from the powerhouse law firm Sullivan & Cromwell. “Now it was part of my day to day, and the office wasn’t big.”

Many former employees recalled hearing Ms. Kaplan berating colleagues for their supposed incompetence and lack of intelligence. (Most would speak only on the condition that The Times not identify them, citing fear of professional repercussions.)

In the midst of the #MeToo movement, Ms. Kaplan told colleagues that she was too smart to ever have been sexually assaulted, according to Seguin Strohmeier, another early hire, and two other former associates who also heard the remarks.

Ms. Kaplan’s lawyers said in a letter to The Times that she had never “suggested that anyone can be ‘too smart’ to be sexually assaulted because that is obviously not true.”

Five employees at the firm recalled inappropriate comments Ms. Kaplan made about colleagues’ looks. Once, she told a female associate that the associate was more suited to “back of house” work because of her appearance. Another time, Ms. Kaplan said the same associate was too much of a “dyke” to clerk for the Supreme Court, Ms. Strohmeier recalled. Other times she used gender-specific insults.

Ms. Kaplan’s lawyers denied that she criticized employees’ appearances and said she “is hardly the only experienced trial lawyer prone to salty language at times.”

Many former employees recalled Ms. Kaplan’s publicly berating case managers, who are young, low-ranking employees. Once she verbally attacked a case manager who disobeyed her command not to include meatballs in a pizza order. Ms. Kaplan’s fury was so remarkable that a lawyer took notes, which The Times reviewed. The notes described the meatball incident as one of a few examples in which Ms. Kaplan “publicly derided” the case manager “both to her face and behind her back.”

Mr. Clark and Ms. Tent, the lawyers for Ms. Kaplan, said this was inaccurate. “To the extent Ms. Kaplan gave instruction about what food to order, it was typically to order too much rather than too little food,” they wrote.

To the frustration of some colleagues, Ms. Kaplan at times insisted that she review in advance certain emails that partners planned to send externally. On occasion, she became irate when this edict was violated.

An Open Secret

By the 2020 election, Ms. Kaplan’s conduct had become something of an open secret in the legal community. That fall, a coalition of progressive groups prepared a list of ideal candidates for judicial nominations to send to the incoming Biden administration. Ms. Kaplan was on an early version of the list, according to a copy reviewed by The Times.

But before it was sent, Ms. Kaplan’s name was deleted at the behest of Molly Coleman, a lawyer and a founder of the People’s Parity Project, whose goals included eliminating harassment and discrimination in law. Ms. Coleman said in an interview that she had heard from lawyers at Kaplan Hecker & Fink who wanted to leave because of workplace conditions. She told other people in the coalition that if Ms. Kaplan was nominated for a judgeship, her organization would publicly oppose her. She said no one had objected to removing Ms. Kaplan from the list.

Ms. Kaplan’s lawyers said she could not comment as she was not aware of being on any such list and did not know if she had been taken off one.

Near the end of 2021, Ms. Kaplan’s lawsuit against the white supremacists in Charlottesville went to trial. It was a high-stress environment; Ms. Kaplan was targeted with antisemitic threats. She told some attorneys on the multi-firm team that they didn’t deserve their law degrees. She threatened to ruin one’s career.

As the trial was ending, Ms. Kaplan’s co-counsel from Paul Weiss, the veteran trial lawyer Karen Dunn, called out Ms. Kaplan’s behavior during a heated meeting, saying she had never seen another lawyer treat people so poorly, according to lawyers who witnessed the argument.

Ms. Dunn declined to comment. Ms. Kaplan’s lawyers denied that the incident had taken place and disputed the accounts of her behavior during the trial.

Ms. Kaplan and her team won the Charlottesville case: The jury found the “Unite the Right” rally organizers liable for more than $25 million in damages. The lawyers were proud of the win. But at least five of them later left Kaplan Hecker & Fink.

A Signature Issue

When the #MeToo movement erupted in October 2017, only a few months after the firm was founded, Ms Kaplan quickly made it a signature issue. She lobbied for legal changes that would make it easier for survivors to sue their assailants and eventually became the chairwoman of Time’s Up, the celebrity-studded nonprofit organization that fought sexual harassment in the workplace, and co-founded its legal defense fund.

But Ms. Kaplan wasn’t representing only victims. She defended Goldman Sachs and Riot Games in lawsuits related to sex discrimination. She also helped companies like Uber, the parent company of Pornhub and Vice Media improve their practices in the wake of sexual misconduct scandals. A former senior employee said the firm’s pitch to such clients was that Ms. Kaplan’s credibility on #MeToo would help them handle their crises, which made some at the firm uncomfortable.

“It is fully consistent with the firm’s work in this space to support investigative and reform projects,” Ms. Kaplan’s attorneys said.

There was only one occasion when the tension between Ms. Kaplan’s public advocacy and private legal practice threatened to become a serious problem.

In 2020, when Gov. Andrew M. Cuomo of New York faced allegations of sexual harassment, he turned to Ms. Kaplan for advice on how to confront the crisis. Ms. Kaplan’s role became public months later when the New York attorney general released a report detailing the investigation of Mr. Cuomo’s actions.

The backlash was intense. More than 150 victims and advocates signed an open letter to the Time’s Up board accusing it of prioritizing “its proximity to power over mission.” Ms. Kaplan soon resigned as chairwoman.

In public, she seemed to weather the fallout. Inside the firm, though, the fracas over Ms. Kaplan’s entanglement with Mr. Cuomo continued to rankle, causing increasing doubts among some lawyers about her judgment.

At least one client in a #MeToo case reached out to the firm, writing in an email reviewed by The Times: “Most distressing is the realization that Kaplan Hecker may be using pro bono cases like mine, and in particular cases representing sexual violence victims, in order to launder the firm’s reputation and purchase credibility with which they can more effectively market themselves as paid representatives for perpetrators and enablers.”

Ms. Kaplan’s lawyers said the client who had sent the email kept Ms. Kaplan as a lawyer. They added that the firm did an “extraordinary” amount of pro bono work.

Agreeing to Step Down

It was shortly before Thanksgiving last year when Mr. Hecker and Ms. Fink, as well as other partners at the firm, informed Ms. Kaplan that it was no longer viable for her to remain on the management committee that oversaw and made crucial decisions about the firm.

The partners remained worried about her treatment of colleagues, and they viewed her as playing an obstructionist role that was interfering with key decisions at the firm, according to people familiar with the internal dynamics.

Mr. Hecker and Ms. Fink recognized that pushing Ms. Kaplan off the committee was essentially sidelining her and might lead her to quit the firm, according to a person familiar with the decision-making.

Ms. Kaplan agreed to step down from the committee. She framed the decision as voluntary and noted that it gave her more time to prepare for the fast-approaching defamation trial that would pit her client Ms. Carroll against Mr. Trump.

By the time the trial got underway in Lower Manhattan in January, Ms. Kaplan had already begun mulling her departure. The firm had grown quickly, and she longed for a “return to my roots,” as she later put it, with a smaller and more focused law firm.

It wasn’t until months later, in April, that many of the partners knew that she would be leaving the firm that she created seven years earlier.

On Monday, her name will be removed from the law firm, which will now be known as Hecker Fink.