The former spy at the centre of the Partygate scandal made an enemy out of Prince Harry - and received a humiliating nickname.
Simon Case has been dubbed "the most important man in politics you've probably never heard of" and became the UK's most senior civil servant.
In his current job as Cabinet Secretary, the powerful but largely invisible figure has served three different prime ministers - and has recently called Boris Johnson's claims into question.
In written evidence given to the cross-party privileges committee, Case denied giving Johnson any reassurances that Covid rules and guidance were followed at all times in No 10.
Case was also embroiled in the Matt Hancock WhatsApp leak saga, as he asked how many people had been "locked up" in quarantine hotels and said: "I just want to see some of the faces of people coming out of first class into a Premier Inn shoe box."
Before he became "the most indiscreet man in government" and a Lockdown Files casualty, he was actually working for Prince William as his private secretary.
A former colleague at Kensington Palace said Case took the job to indulge his fascination with how the British state works - and because it was a rare chance to work in such a senior royal role.
Case worked as an advisor to the heir to the throne, offering practical and emotional support to William, who he is said to have had a good relationship with.
He joined the Prince of Wales on high-profile trips, was chief of staff to the household and had to maintain communication between the various royal palaces.
The biggest controversy during his time as William's private secretary was Prince Harry and Meghan Markle's decision to stand down as working royals and move to North America.
By Harry's own account, he did not get on well with William's man and referred to him in his book Spare as 'The Fly'.
While Case is not named, he is strongly believed to be 'The Fly' as he was William's private secretary during the dates mentioned.
In Spare, Harry explains that he spent his life dealing with courtiers but now it is mostly just three "middle-aged white men" who had consolidated power "through a series of bold Machiavellian manoeuvres".
As well as 'The Fly, he also mentions 'The Bee' and 'The Wasp', so there's a clear insect trend.
They are believed to be the codenames for the late Queen's private secretary, Sir Edward Young and King Charles' private secretary, Clive Alderton, respectively.
Describing them as "usurpers", Harry adds: "Deep down, I feared that each man felt himself to be the One True Monarch, that each was taking advantage of a Queen in her nineties, enjoying his influential position while merely appearing to serve."
Harry claims that all three men considered him "irrelevant" at best and "stupid" at worst.
The Duke of Sussex went to The Bee and The Wasp to speak about his struggles and they supposedly agreed to help, but Harry claims nothing ever happened.
However, The Fly is the only one that Harry didn't seek an audience with - and Harry was particularly scathing.
"The Fly had spent much of his career adjacent to and, indeed drawn to, s***. The offal of government and media and wormy entrails, he loved it, grew fat on it, rubbed his hands in glee over it, though he pretended otherwise," writes Harry.
Harry says the Fly wanted to give the impression he was very casual and above the squabbles.
Although it isn't all negative, as he does describe his William's advisor as coolly efficient and ever helpful.
Once he finished working for the Palace, Case went back into Downing Street under Johnson - and he has now worked for three different PMs.
But Case's reputation has been damaged by a number of controversies, including the Hancock WhatsApp leak earlier this month.
The head of the civil service warned Brits might not listen to "nationally distrusted" Johnson during the pandemic.
In messages leaked to the Telegraph, Mr Hancock writes: "I am going to get stuck in and drive this roll out. The PM is completely right on this. Delegate delegate delegate."
Mr Case agrees: "My concern is that we can figure out how to test, what we don't know how to do is get people to isolate.
"We are losing this war because of behaviour - this is the thing we have to turn around (which probably also relies on people hearing about isolation from trusted local figures, not nationally distrusted figures like the PM, sadly)."
Mr Hancock replies: "Sure - but even with a massive rocket up them the lorries won't roll until late next week - so we can fix the new isolation rules between now and then".
In June 2020, Mr Case also suggested that getting Mr Johnson to focus on daily case numbers "keeps him honest".
The civil service boss faced criticism when the leaked messages revealed he joked with ministers about locking travellers up in hotel quarantine.
In February 2021, Mr Hancock said they were planning on "giving big families all the big suites and putting pop stars in the box rooms" when travellers returning to the UK were forced to isolate in Government hotels.
Mr Case replied: "I just want to see some of the faces of people coming out of first class into a Premier Inn shoe box."
A few days later, he asked how many people had been "locked up" in hotels the previous day.
Mr Hancock replied: "None. But 149 chose to enter the country and are now in Quarantine Hotels due to their own free will!" to which Mr Case replied: "Hilarious."
