Bob Quick's "laid-back" style has landed him in trouble before
Bob Quick has resigned as the country's most senior counter-terrorism officer, after mistakenly revealing a secret terrorism document to photographers as he arrived at Downing Street.
Following the error, he said he believed his position was "untenable".
While colleagues and politicians alike agreed that he was right to go, he has been widely praised for the work he did as the head of one of the most challenging fields in UK policing.
While it may come as little comfort, many have also commented on his integrity in facing up to his error and resigning with speed and decisiveness.
In recent months Bob Quick - a father of five - has been no stranger to controversy. His resignation comes just three months after he was criticised over the arrest of Tory MP Damian Green, as part of an ongoing inquiry into leaks from the Home Office.
Quick by name he is, but patient and considered by nature, say colleagues.
The assistant commissioner had been regarded as a steady, safe pair of hands.
One colleague described him as "calm and collected... a really, really decent man, whose integrity is without question".
Reacting to his resignation Sir Ken Jones, president of the Association of Chief Police Officers (Acpo), said Mr Quick had shouldered his "immense responsibilities" as head of counter-terrorism, without shirking.
"He has orchestrated and led a number of critical counter-terror operations over the past year or so and we are all the safer for that," he said.
Both the home secretary and the prime minister - who received an apology from Mr Quick - thanked him for his contribution.
A graduate of both Exeter and Cambridge universities, Bob Quick joined the police in 1978.
He worked in the Metropolitan force as a detective, investigating murders and other serious violent crimes, before being appointed head of the Met's anti-corruption command - a post reserved for officers who are deemed to be whiter than white.
An indication of Mr Quick's patient, considered approach to policing came in December 2002, when he took charge of a police operation in east London to deal with a gunman who had taken a hostage at a flat in Hackney.
Mr Quick, a commander at the time, was widely praised for the restraint shown by police during the operation, London's longest armed siege.
It ended after 15 days when the gunman, Eli Hall, shot himself, before fire took hold of the flat. No-one else was hurt.
The following year, Mr Quick was promoted to deputy chief constable of Surrey Police, where he landed the top job in 2004.
One of his first acts on his appointment was to hold a series of roadshows, where officers and staff could question him about aspects of the job.
It set the tone for his period in charge, where he pioneered the use of civilian staff to carry out back-office functions traditionally performed by fully sworn officers.
As the national lead of the Association of Chief Police Officers on workforce modernisation, Mr Quick built a reputation as a police officer who was prepared to, and able to, think "outside the box".
The approach clearly impressed the Home Office, and in March 2008 he was promoted again - to head Scotland Yard's counter-terrorism and security department, Specialist Operations.
For the first eight months, Mr Quick went about his job quietly and efficiently.
There were few headlines, no off-the-cuff briefings to journalists or extravagant claims about what he could or would do.
Instead, Mr Quick began a programme to forge closer links with Muslim communities, as part of the government's "prevent" strand of its anti-terrorism strategy, although not everyone was said to be fully signed up to the approach.
The Damian Green affair changed things in terms of his public profile, in December 2008.
After the initial arrest he later had to apologise to the Conservative Party when a row blew up over a newspaper article about Mr Quick's wife's luxury car firm.
He had accused the party of mobilising the media against him to undermine the leaks inquiry but later retracted his allegations.
Some say Mr Quick's own style, described as "relaxed" and "laid back", may have got him into trouble on that occasion.
It was suggested that when he ordered the arrest of Damian Green, and the search of his offices, he did not see the political storm it would cause, said the BBC's Danny Shaw.
The inevitable result of being at the centre of such a storm is that every aspect of one's life is examined.
But he was perhaps caught off-guard when a reporter questioned him about the subsequent Mail on Sunday story on his wife's business.
His comments to the reporter - making allegations about the Tories' role in the affair - were said to be uncharacteristic of him.
The terrorism documents incident was again a basic error, that could have had devastating consequences on the anti-terrorism operation that was being planned.
As soon as it happened Bob Quick knew - as all those around him did - that he would have to go.
But after the news was announced there was little initial evidence of a gleeful response from any quarter, with London Mayor Boris Johnson saying he had accepted the resignation with "great reluctance and sadness".