The prime minister's chief adviser, Dominic Cummings, has quit following reports of internal turmoil at Downing Street.
For someone with a supposedly backroom role, Mr Cummings has achieved remarkable prominence, and indeed notoriety.
His lockdown trip to County Durham became the stuff of social media legend, dominating the tabloid front pages and the national conversation for days.
It also succeeded in putting the historic market town of Barnard Castle on the map.
Mr Cummings revealed he had visited the town, with his family, to test his ability to drive back to London, after experiencing loss of vision due to coronavirus.
This explanation - which launched a thousand memes - came during an unprecedented press conference in the Downing Street garden to explain the reasons why he chose to travel to his parents' County Durham farm in March - at a time when he believed both he and his wife were about to be laid low with coronavirus - in order to guarantee his four-year-old son's safety.
"I don't regret what I did," he told journalists. "The situation I was in was exceptional circumstances. I think I behaved reasonably."
Boris Johnson stood by his adviser throughout this episode - to the consternation of some of his supporters, who feared it was undermining his attempts to hold the country together in the face of arguably one of the biggest peacetime threats it has faced. Not to mention burning through the political capital, and goodwill, he had generated months earlier at a triumphant general election.
But it is hard to overstate how important Mr Cummings was to the Johnson project.
The two are very different characters - Mr Johnson likes to be popular, Mr Cummings appears indifferent to such concerns - but they formed a strong bond in the white heat of the 2016 Vote Leave campaign to get Britain out of the EU.
The combination of Mr Johnson, the flamboyant household-name frontman, with Mr Cummings, the ruthless, data-driven strategist, with a flair for an eye-catching slogan, proved to be unbeatable.
Mr Cummings was credited with the "take back control" slogan that appears to have struck a chord with so many referendum voters, changing the course of British history.
It still surprised some when Mr Cummings was brought into the heart of government as Mr Johnson's chief adviser, when he became PM, given his past record of rubbing senior Tory politicians up the wrong way.
But it proved to be a shrewd move. It was Mr Cummings who devised the high-risk strategy of pushing for an election last year to be fought on a "Get Brexit Done" ticket, focusing on winning seats in Labour heartlands, something no previous Tory leader had managed to do in decades.
Many of the policy ideas that have shaped the Johnson government's agenda have his fingerprints all over them.
"Levelling up" - moving power and money out of London and the South East of England - is a Cummings project, as are plans to shake-up the civil service, take on the judiciary and reform the planning system.
The team around Mr Cummings at Downing Street, some of whom are Vote Leave veterans, are fiercely loyal to him and share with him a sense that they are outsiders in Whitehall battling an entrenched "elite".
There have been tales of crackdowns on special advisers suspected of leaking to the media and angry, dismissive behaviour towards Tory MPs, civil servants and even secretaries of state.
But the "Vote Leave gang", as they are disparagingly referred to by their enemies, have seen their power curtailed dramatically in recent days, amid battles with those around the PM who don't like their abrasive, confrontational style.
The departure of Mr Cummings' Vote Leave ally, director of communications Lee Cain, led to rumours that he too would be heading for the exit.
He denied them, but said his "position hadn't changed" since he suggested he would complete his government work by the end of 2020. But he has now left his role after a conversation with Mr Johnson.
None of this will have come as much of a surprise to veteran Cummings watchers.
'Weirdos and misfits'
He has been in and around the upper reaches of government and the Conservative Party for nearly two decades, and has made a career out of defying conventional wisdom and challenging the established order.
He has never been a member of the Conservative Party and has little time for what he sees as some of the time-servers and publicity addicts that populate the Commons benches.
A longstanding Eurosceptic who cut his campaigning teeth as a director of the anti-euro Business for Sterling group, Mr Cummings's other passion is changing the way government operates.
He grabbed headlines when he posted an advert on his personal blog for "weirdos and misfits with odd skills" to work in government.
The career civil servants and "public school bluffers" in Whitehall are singularly ill-equipped to take decisions about complex issues, he has argued at great length on his blog.
Instead, he believes, mathematicians and data scientists should be given a far bigger role - and he has made an effort to educate himself in these fields.
As the world now knows, Mr Cummings is a native of Durham, in the North East of England. His father, Robert, was an oil rig engineer and his mother, Morag, a teacher and behavioural specialist.
He went to a state primary school and was then privately educated at Durham School. He graduated from Oxford University with a first-class degree in modern history and spent some time in Russia, where he was involved with an ill-fated attempt to launch an airline, among other projects.
After a stint as campaign director for Business for Sterling, he spent eight months as chief strategy adviser to then Conservative leader Iain Duncan Smith.
He played a key role in the 2004 campaign against an elected regional assembly in his native North East.
In what turned out to be a dry run for the Brexit campaign, the North East Says No team won the referendum with a mix of eye-catching stunts - including an inflatable white elephant - and snappy slogans that tapped into the growing anti-politics mood among the public.
He is then said to have retreated to his father's farm, in County Durham, where he spent his time reading science and history books in an effort to attain a better understanding of the world.
He re-emerged in 2007 as a special adviser to Michael Gove, who became education secretary from 2010 and turned out to be something of a kindred spirit. The pair would rail against what they called "the blob" - the informal alliance of senior civil servants and teachers' unions that sought, in their opinion, to frustrate their attempts at reform.
He left of his own accord to set up a free school, having alienated a number of senior people in the ministry and the Conservative Party.
He once described Brexit Secretary David Davis as "thick as mince" and as "lazy as a toad" and irritated David Cameron, the then prime minister, who called him a "career psychopath".
His appointment as head of the Vote Leave campaign - dramatised last year in Channel 4 drama Brexit: The Uncivil War - was seen as a risk worth taking by those putting the campaign together but he left a controversial legacy.
Vote Leave was found to have broken electoral law over spending limits by the Electoral Commission and Mr Cummings was held in contempt of Parliament for failing to respond to a summons to appear before and give evidence to the Culture, Media and Sport Select Committee.
On the few occasions he has been scrutinised by MPs, there have often been rhetorical fireworks and bad blood on both sides.
He has given few clues as to what he will do after quitting his Downing Street role, but it seems unlikely that we have heard the last of him.