LONDON — Prime Minister Boris Johnson's chief adviser — dubbed "Boris's brain" by the British press — walked out the front door of 10 Downing Street carrying a cardboard box Friday, seeming to confirm rumors of his imminent departure.

He could have left out the back door. Or without the trappings of a move. And so the theatrical show, staged for banks of news photographers, was widely seen as an acknowledgment that the political strategist who was instrumental to Brexit and to Johnson's rise was officially out.

Usually the outside world cares little for the fate of a special adviser in the British bureaucracy, but Cummings, 48, is no ordinary aide. He's the best-known adviser in recent memory, whose exploits alongside Johnson have made him a household name in England.

His departure — or his ousting — dominated British front pages and news sites Friday, beating out the death of the 1970s-era serial killer the Yorkshire Ripper, who succumbed to covid-19.

Cummings served as campaign director of the “Vote Leave” campaign in 2016 and is credited with the memorable slogan “Take back control.” His real-life role in the Brexit drama was turned into a movie, “The Uncivil War,” in which Cummings is played as an evil genius in a hoodie by actor Benedict Cumberbatch.

Later, the political strategist helped Johnson win the 2019 general election in a landslide, marching his boss to an 80-seat majority in Parliament under the banner “Get Brexit done.”

Cummings’s exit follows that of his fellow arch-Brexiteer, Lee Cain, a former tabloid journalist who became Johnson’s communications director and chief spin doctor. Cain quit this week after he lost a power struggle over the chief of staff job.

The departures mark a profound tilt in the axis of power among Johnson’s inner circle. Brussels diplomats were wondering aloud whether Johnson might soon erase his red lines to ink a post-Brexit free-trade deal with the European Union.

As the palace intrigue at the prime minister’s 10 Downing Street offices unfolded this week, Cummings insisted that he had not been shoved out but was fulfilling his earlier promise to make himself “largely redundant” by the end of 2020.

BBC political editor Laura Kuenssberg reported Friday that Cummings told her that “rumors of me threatening to resign are invented.”

However, she added, a Downing Street insider told her that Cummings “jumped because otherwise he would be pushed.’ ”

According to British newspapers, Carrie Symonds, Johnson’s 32-year-old fiancee and former Conservative Party communications director, played a pivotal role in changing the top jobs at Downing Street.

In its take, the Telegraph reported how “ ‘Carrie’s Crew’ saw off the ‘Brexit Boys.’ ”

Cummings is a polarizing figure, celebrated as a target-
focused strategist who thinks big and condemned as a pugnacious iconoclast who fancies himself smarter than he is.

Alongside Johnson, Cummings hoped to transform a clubby British bureaucracy into a streamlined machine powered by science and data. But he also ran headlong into Conservative Party backbenchers in the House of Commons, who took a distinct disliking to him.

John Major, a former Conservative prime minister and ­anti-Brexiteer, said in a speech last year: “I offer the prime minister some friendly advice: Get rid of these advisers before they poison the political atmosphere beyond repair. And do it quickly.”

Cummings was at the center of another political storm this year, when he and his wife, both having tested positive for the coronavirus, fled their London home to travel 260 miles to a family farm.

His apparent flouting of strict lockdown rules at the peak of the pandemic raised questions about fair play and cost Johnson public support. Cummings said he had done nothing wrong, maintaining that he drove north so a relative could care for his young son if he and his wife — a top editor at the Spectator magazine and daughter of a baronet with a castle — were both sick in bed.

Even tabloids that traditionally back Conservative leaders derided Cummings and Johnson, with the Daily Mail’s front page asking, “What Planet Are They On?”

Cummings was further mocked for taking a short trip to scenic Barnard Castle while he was supposed to be in isolation — to test his eyesight, he claimed. Critics of Johnson and Cummings saw hypocrisy: one rule for elites, another rule for the rest.

Jill Rutter, a senior fellow at the Institute for Government, an independent think tank, credited Cummings as “a very influential figure in shaping this government.” His departure leaves a vacuum, she said, especially with a leader like Johnson, who isn’t an ideological politician.

“With Margaret Thatcher, did it matter who her advisers were? Not so much,” she said. “Thatcher set the tone; people came to her to help define her project. Boris Johnson, on the other hand, is more defined by the people around him.”

Cummings and others from the pro-Brexit team who were in Downing Street took pride in the fact that they were not Conservatives and didn’t care much for Conservatives in Parliament, Rutter said.

“That’s been a big source of tension,” she said.