Sir Ian Blair had a baptism of fire
"You don't come into here without a pair of copper-bottomed trousers", said Sir Ian Blair after he became commissioner of the Metropolitan Police in February 2005, "this is a very tough place".
Within five months of starting the job, he found out just how tough it was.
Two waves of bomb and attempted bomb attacks on London during July 2005 sparked a swift criminal investigation and several arrests.
While the police tracked down the 21 July bombers, firearms officers also shot dead Jean Charles de Menezes after believing the Brazilian to be one of their suspects.
Since that terrible day, Oxford-educated Sir Ian has been dogged by repeated calls from critics for him to go.
Lately there has been a succession of internal rows over race relations - and claims of the commissioner's personal involvement in how a contract was awarded.
Throughout these turbulent three years, Sir Ian has been accused of thinking like a politician rather than a policeman - and it was politics that was his undoing.
The battle over Sir Ian's future began in the aftermath of the shooting dead of Brazilian electrician Mr de Menezes. The Metropolitan Police was found guilty of breaching health and safety laws over the Brazilian's death.
No individual officer has faced charges over the killing at Stockwell Underground station. Sir Ian himself was cleared of wrongdoing over claims that he misled the public about what the police knew on the day.
Sir Ian was educated in Shropshire and Los Angeles and went on to be a contemporary of former prime minister Tony Blair at Oxford University.
He was a graduate recruit to the Metropolitan Police in 1974 and enjoyed a swift rise through the ranks from his first constable beat in central London's Soho.
By 1985 he had become a detective chief inspector in north London and was responsible for the identification of the victims of the King's Cross station fire two years later.
Sir Ian went on to head Operation Gallery, the largest inquiry into police corruption in London for a decade.
During the 1980s he published a book which made a significant contribution to changing the way in which police investigate rape. Senior management postings with both Thames Valley and Surrey Police prepared him for the top policing job in the country.
In May 2000 he returned to the Met as the number two after losing out to Sir John Stevens for the top job.
Over four years, during which he was knighted, he began behind-the-scenes work to reshape the police.
He took over the top job in February 2005.
Sir Ian was a leading architect in the creation of the controversial community support officers and has been heavily involved in the wider agenda to modernise policing for the 21st Century.
He has also been a driving force behind the widely praised "neighbourhood policing" strategy that dedicate small teams of officers to local areas.
Crucially, he was at the forefront of the government's attempts to overhaul national security strategy in the face of increased terrorist threats.
But among many rank-and-file officers he is regarded as a politician rather than a copper with the street beats at heart.
As he made enemies among his ranks, some of these senior officers began briefing against him, telling both journalists and politicians that Sir Ian was not the right man for the job.
Supporters of Sir Ian have touted him as a campaigning man who has worked hard to end the alleged casual sexism and racism of the service's "canteen culture". He presided over both a significant fall in crime in the capital and a vital overhaul of national counter-terrrorism strategy.
They said he was a man capable of dragging the police into the 21st century while, at the same time, having the support of ministers. Enemies said he was too close to Labour for comfort - a man who enjoyed the corridors of power more than the corridors of New Scotland Yard.
But once accusations turned to claims of corruption and a crisis in relations with some top officers the end was, perhaps, inevitable.
Boris Johnson, the new Conservative mayor of London, had made it clear that he wanted a fresh approach to policing. And when he took over as chairman of the Metropolitan Police Authority, the oversight body, he told the commissioner it was time for a change.
The commissioner didn't want to go and the mayor had no powers to remove Sir Ian. But it was one political battle that the policeman concluded he could not win.
Sir Ian once said: "I am not a lame duck commissioner. I am not in the position of being in office but not in power."
But the reality was for much of his time in New Scotland Yard, Ian Blair fought to defend his reputation. His attempt to cling to office was ultimately futile; confidence drained away, friends beyond government were hard to find.