Sir Ronnie Flanagan was appointed Her Majesty's Chief Inspector of Constabulary in 2005.
But he is perhaps best known for his former job in his native Northern Ireland, where he was Chief Constable of both the Police Service of Northern Ireland (PSNI) and the Royal Ulster Constabulary.
Sir Ronnie Flanagan worked in Northern Ireland for more than 30 years
He stood down as Chief Constable of the PSNI in 2001 after five years in the post.
During his time at the helm, Sir Ronnie presided over some of the biggest changes in policing and witnessed some of the most significant events in Northern Ireland's recent history, including the Good Friday Agreement and Omagh bomb.
As chief constable for the old RUC since 1996 and of the PSNI from November 2001, he was the well-established public face of policing and used to the way views about the policing of a divided community twist and turn.
He was seen as "damaged goods" to one community, "impartial and professional" to many in the other.
Such was the gulf between unionists and nationalists in their view of the head of policing in Northern Ireland.
But few believed that anyone other than Sir Ronnie could have coaxed and nursed the RUC through such a painful period of change - both symbolic and structural.
Sir Ronnie, an RUC man for 31 years, felt the pain personally but pushed through the reforms.
In October 2000, he said the change of the name of the force to the PSNI would cause "great hurt" to officers.
"I understand the feelings of my members because I share those feelings," he said.
He added that he was not convinced that the changes to the RUC title would attract more Catholics into the force and bring about the acceptance of Northern Ireland's police force by the nationalist community that Chris Patten's report promised.
"If we are to endure this great hurt proposed then I hope the gains envisaged are demonstrable and achievable."
The Patten Report was published in 1999 and was one of the main elements of the Good Friday Agreement peace accord.
In the same year, Sir Ronnie acknowledged the awarding of the George Cross to the RUC.
He said: "It is the most momentous recognition of past achievement and the most immense incentive to us all now and in future to continue to provide the highest quality police service to all our people in Northern Ireland."
Sir Ronnie joined the RUC in 1970 and six years later had been promoted to the rank of inspector.
Twenty years into his policing career he was a chief superintendent and had moved to the Police Staff College at Bramshill as director of the Intermediate Command Course and then the Senior Command Course, designed to prepare selected officers for chief officer rank.
He achieved this rank himself in 1992 when promoted to assistant chief constable.
He was the RUC's senior commander in Belfast in 1993 at the time of the Shankill bomb and in a period when the city experienced some of the worst violence for many years.
He later became head of special branch and was promoted to deputy chief constable in February 1996.
That same year Flanagan conducted the RUC's Fundamental Review of Policing. In November 1996 he was Sir Hugh Annesley's successor as chief constable.
Sir Ronnie holds a Bachelor of Arts degree and a Master of Arts degree in administrative and legal studies and is a graduate of the FBI Academy.
He was awarded the OBE in 1996 and received a knighthood three years later.
He has given security advice to various secretaries of state and, in 1998, both the Ulster Democratic Party and Sinn Fein were suspended from the Good Friday Agreement negotiations when he linked the UDA and the IRA to a number of murders.
The row between the police ombudsman and the chief constable over the Omagh bomb investigation developed into a bitter public clash.
The row over the investigation into the 1998 Real IRA bomb, which killed 29 people and injured more than 200, was sparked by a critical report in December by Police Ombudsman Nuala O'Loan.
Mrs O'Loan made a recommendation that an officer from a force outside Northern Ireland should be brought in to head the inquiry.
However, the chief constable was critical of the ombudsman's report, describing it as "flawed" and he rejected the request and instead appointed a senior officer from Merseyside as an adviser.
The new Policing Board was forced to resolve the row and decided to appoint a senior officer from England to oversee the investigation into the Omagh bombing.
His departure from office in 2001 was also marred by the embarrassment of a breach of security at a key Special Branch office at the Belfast police headquarters.
In June 2002, Sir Ronnie became the first person in Northern Ireland to receive a Knight Grand Cross of the Order of the British Empire (GBE) in the Queen's Birthday Honours List. He was honoured for managing the changeover from the RUC to PSNI.
In 2002, he became one of Her Majesty's inspectors and three years later, at the age of 55, he was put in charge.
At the time, then Home Secretary Charles Clarke said: "Sir Ronnie has a proven record of operational and managerial achievement at the highest levels of the police service.
"His long involvement in policing - both as an officer and as an Inspector of Constabulary - means he is well place to advise ministers, the Home Office and other tripartite partners on policing issues."
As an inspector, he wrote the report into the Soham murder investigation, which accused Cambridgeshire Constabulary of losing momentum after the good response initially.
The UK government also sent him to Iraq to carry out a review of policing there.
Earlier this year, he came in for criticism after Northern Ireland's police ombudsman found officers colluded with loyalists behind more than a dozen murders in north Belfast at a time when he was in charge.
He said he had no knowledge of any such collusion.