Until a few days ago, it seems fair to say that hardly anyone in the UK had heard of Sue Gray.
Now, her name is in every newspaper and she is a meme on social media, the prime minister's future quite possibly in her hands.
On Wednesday, Johnson gave a partial apology for attending a "bring your own booze" party in No 10's garden on 20 May 2020.
So, who is Sue Gray- once described by former cabinet minister Oliver Letwin as the person who "runs" the UK.
She was permanent secretary of the Department of Finance in Northern Ireland from 2018 to 2021, and is now second permanent secretary in the Cabinet Office.
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Her reputation appears to be very strong.
Cabinet reshuffles, departmental reorganisations, the whole lot- it's all down to Sue Gray.
Sir David Normington, a former Whitehall permanent secretary, said that among civil servants Sue Gray is the "best person" to lead the current inquiry.
"She will be very aware that she has the reputations and possibly the careers of senior civil servants and possibly of the prime minister in her hands.
Once she has reported, it will be up to the prime minister, other ministers and MPs to determine what happens next.
"The prime minister himself gets to decide if he needs to be investigated under the ministerial code.
Gray, a senior civil servant, was appointed last month to examine claims that Downing Street officials broke Covid rules by holding a series of parties and events during the pandemic.
In December 2021, the UK's top civil servant Simon Case stepped down from leading this same inquiry into the parties when it emerged one had been held in his own office.
Keir Starmer, the Labour leader, accused Johnson of breaking the ministerial code by making misleading statements in a series of denials about parties at No 10.
Afterwards, several Tory MPs privately said they would await the Gray findings and, if damning, call for their prime minister to quit.
However, Dave Penman, the head of the FDA union, which represents senior civil servants, said if Gray makes a recommendation for further inquiries under the ministerial code, Johnson still has the power to block it.
Bob Kerslake, the former head of the civil service, said he had previously been happy for the inquiry to be run by Case but believed the latest revelations meant a retired judge should be asked to receive Gray's findings.
The findings could decide whether they stay in their jobs or not.
Sir David Normington, who worked at the Home Office and oversaw public appointments, said Gray had been placed in a "very odd" position as the public waited for her verdict.
"She's in the middle of a political maelstrom at the moment, trying to establish the facts, and there ’ ll be a lot of pressure on her to conclude this investigation as quickly as possible," he said.
That is a very difficult position to be in, however fair and fearless and rigorous you are."
Boris Johnson has admitted he attended a recently-revealed gathering at 10 Downing Street on 20 May 2020, saying he was there for 25 minutes.
First of all, when it comes to civil servants investigating Conservative parties during Covid- the recent track record isn't great.
In 2015, as the government's director general of its propriety and ethics team, she was described as "the most powerful person you 've never heard of".
In 2017 she was responsible for the sacking of Damian Green, a close ally of then-Prime Minister Theresa May, because of "inaccurate and misleading" statements over what he knew about claims porn was found on his office computer.
And yes, I wanted to have change," she told the BBC at the time.
So next time you 're asked a question you don't want to give an answer to, you could try responding with a simple "Sue Gray is investigating" and see how far that gets you.
But it is becoming increasingly clear that his party is running out of patience.
The Scottish Tory leader Douglas Ross became the first MP to break cover and call for Johnson to go, saying his position was "untenable" after he conceded attending the “ bring your own booze ” party during lockdown.
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