Shortly after Jonathan Kanter took over the Justice Division’s antitrust division in November 2021, the company secured an extra $50 million to research monopolies, bust prison cartels and block mergers.

To have fun, Mr. Kanter purchased a prop of an enormous verify, positioned it outdoors his workplace and wrote on the verify’s memo line: “Break ’Em Up.”

Mr. Kanter, 50, has pushed that philosophy ever since, changing into a lead architect of probably the most important effort in many years to combat the focus of energy in company America. On Thursday, he took his largest swing when the Justice Division filed an antitrust lawsuit in opposition to Apple. Within the 88-page lawsuit, the federal government argued that Apple had violated antitrust legal guidelines with practices supposed to maintain clients reliant on its iPhones and fewer more likely to swap to competing units.

That lawsuit joins two Justice Division antitrust instances in opposition to Google that argue the corporate illegally shored up monopolies. Mr. Kanter’s workers has additionally challenged quite a few company mergers, together with suing to cease JetBlue Airways from shopping for Spirit Airways.

“We need to assist actual folks by ensuring that our antitrust legal guidelines work for staff, work for customers, work for entrepreneurs and work to guard our democratic values,” Mr. Kanter stated in a January interview. He declined to touch upon the Google instances and different lively litigation.

At a news conference concerning the Apple lawsuit on Thursday, Mr. Kanter in contrast the motion to previous Justice Division challenges to Customary Oil, AT&T and Microsoft. The swimsuit is aimed toward defending “the marketplace for the improvements that we will’t but understand,” he stated.

Mr. Kanter and Lina Khan, the chair of the Federal Commerce Fee, have now taken motion in opposition to 4 of the six largest public tech corporations, in a sweeping drive to rein within the energy of the business. The F.T.C. has individually filed antitrust fits in opposition to Meta, the proprietor of Fb and Instagram, and Amazon.

However Mr. Kanter and Ms. Khan are on the clock to see how far they’ll take their efforts. The November election might take away President Biden from the White Home and take Mr. Kanter and Ms. Khan with him.

Greater than two dozen individuals who know Mr. Kanter, together with present and former Justice Division staff, described his two-decade rise. Some spoke anonymously to explain confidential authorities deliberations and shows.

Mr. Kanter was raised within the Queens, N.Y., house the place his dad and mom nonetheless reside. After graduating from Forest Hills Excessive Faculty, he attended the State College of New York at Albany after which regulation college at Washington College in St. Louis.

“I grew up in a neighborhood with schoolteachers and law enforcement officials and taxicab drivers and shopkeepers and individuals who labored actually arduous,” he stated, and did so with a “perception that the American dream actually supplied openings and alternatives to comprehend a greater life for future generations.”

He stated he linked antitrust enforcement to these values as a result of “it’s about ensuring that these alternatives can be found to all and ensuring that individuals can succeed on their very own deserves.”

After getting his regulation diploma, Mr. Kanter labored on the F.T.C. earlier than becoming a member of massive regulation companies like Cadwalader, Wickersham & Taft and Paul Weiss. At one level, he represented Microsoft. When the corporate mounted an offensive in opposition to Google, which had eaten its lunch in on-line search, Mr. Kanter made the pitch round Washington that Google deserved extra scrutiny.

He later made related arguments for different Google critics, like Information Corp and Yelp, and stated regulators ought to examine extra tech giants, too. Concurrently, he defended company mergers in separate industries.

Mr. Kanter’s work in opposition to a few of the tech behemoths received him followers amongst those that believed that antitrust legal guidelines had been an important device to make the financial system extra honest.

“Right here was an insider who had additionally come to very related conclusions,” Ms. Khan stated in an interview in November.

After his nomination by Mr. Biden was confirmed, Mr. Kanter, who typically favors formal peak lapels and as soon as wore to a photo shoot an A. Lange & Söhne gown watch that retails for $34,500, debuted his plan for the antitrust division to its workers, folks with data of the presentation stated.

Mr. Kanter branded his initiatives with catchy code names. A plan for the company to shortly weigh in on lively authorized instances obtained the Gen Z moniker “Actual Time AF,” quick for real-time antitrust filings. He known as a plan to research senior company executives the “Billionaire Accountability Venture.”

Mr. Kanter instructed his staff that, at any given second, he wished the division to have the ability to handle 30 civil lawsuits and one other 30 prison instances. He known as the plan “30 for 30.”

The company was already stretched skinny, and a few on the workers felt Mr. Kanter was setting unreasonable objectives, folks with data of the matter stated.

His time in personal apply additionally forged a shadow. Mr. Kanter initially didn’t work on lawsuits in opposition to Google as a result of he had spent years representing its rivals. When he can’t work on instances, together with the problem to JetBlue’s buy of Spirit, they’re led by his principal deputy, Doha Mekki.

Nonetheless, Mr. Kanter has been proactive on the fits in opposition to the tech giants.

As a Google antitrust case over on-line search headed to trial final yr, he instructed authorities attorneys to be extra express and distinguished with their argument that sheer scale of the corporate’s operation entrenched its energy and made it more durable for its rivals to compete, two folks with data of the matter stated. That concept was a central theme when the case was tried in a Washington courtroom final fall. (A ruling is anticipated later this yr.)

Mr. Kanter additionally oversaw the ultimate months of the Justice Division’s investigation into Google’s management of internet marketing expertise. He argued to colleagues that the federal government ought to push for the lawsuit to be determined by a jury as an alternative of a decide, which has been the norm in related civil instances, an individual aware of the matter stated. A jury trial is scheduled to begin in September.

Mr. Kanter’s work has been scrutinized by critics who marvel if he and his compatriots are pushing the boundaries of antitrust regulation too far, hurting the financial system.

William Kovacic, a regulation professor at George Washington College and former chair of the F.T.C., stated Mr. Kanter had but to safe a victory within the form of sweeping monopoly lawsuit that the company was pursuing in opposition to Apple and Google.

“In some methods, he’s nonetheless in search of that extra distinguished trophy to go on the mantelpiece,” he stated. “You win certainly one of these monopolization instances, you possibly can take the remainder of the last decade off.”

Within the January interview, Mr. Kanter defended his push to shift how the company did enterprise. He stated the world had modified radically within the final 30 years. Individuals talk utilizing new mediums, get their info from totally different sources and conduct commerce on ascendant platforms.

“It’s necessary that if we’re going to have antitrust enforcement that’s fit-for-purpose in a contemporary financial system we acknowledge these adjustments,” he stated. “After which we adapt to be sure that we’re implementing the letter of the antitrust regulation and the relevant precedents. However we’re implementing the regulation in a means that displays the realities of at present’s financial system.”

Tripp Mickle contributed reporting from San Francisco. Jack Begg contributed analysis.