The chief constable of Dyfed-Powys Police has retired following claims of alleged financial irregularities.
Terry Grange has retired with immediate effect
The Independent Police Complaints Commission (IPCC) is investigating allegations against Terry Grange, 58, who had held the job since March 2000.
Dyfed-Powys Police Authority said it had accepted "with regret" his retirement with immediate effect.
It said Mr Grange "had indicated that he had allowed his private life to interfere with his professional role".
In a statement, the police authority added: "This has led the police authority to consider the chief constable's position and it was considered to be appropriate to accept his retirement.
"In accepting his retirement, the authority thanked Mr Grange for the leadership which he had brought to the force maintaining its position as one of the best performing in England and Wales."
The IPCC said: "Although the chief constable has now retired the IPCC is continuing its independent investigation into alleged financial irregularities.
"It would be inappropriate for the IPCC to comment further at this stage but it will make a detailed public statement in due course."
The IPCC had announced last Thursday that it was investigating an unnamed Dyfed-Powys officer over "misuse of the police computer system and alleged financial irregularities".
Terry Grange is married with three adult daughters
Joined the Army at 15, serving with the Parachute Brigade
Has a Masters degree in public services
Joined the Metropolitan Police in 1971
Joined Avon and Somerset Police in 1988, becoming assistant chief constable in 1994
Became Dyfed-Powys chief constable in 2000
It has now confirmed that Mr Grange is that officer.
Liberal Democrat MP Lembit Opik, whose Montgomeryshire constituency is in the Dyfed-Powys area, said he was "gobsmacked".
'Bolt out of the blue'
He said: "Whatever the reason for Terry Grange's departure, it must not be allowed to affect the quality of service provision we get from Dyfed-Powys Police.
"Whatever has happened, at a human level I wish Terry the best for the future.
"Frankly, I'm gobsmacked. Terry Grange has been very proactive at involving parliamentarians and talking to us about funding settlements."
Nick Bourne, leader of the Welsh Conservatives, and AM for Mid and West Wales, said Mr Grange had been a "model of rectitude" in all his dealings with him, and paid tribute to his work.
"This comes as a total bolt out of the blue," he said. "In all my dealings with him I found him to be a first-class police officer.
"Obviously I don't know what is behind it, but I'm absolutely stunned."
Mr Grange had served with the Avon and Somerset Constabulary and Metropolitan Police before taking the top job in the predominantly rural part of mid and south-west Wales.
Members of the Dyfed-Powys Police Authority met in private on Monday morning, and it is understood they will meet again on Thursday.
As a member of the Association of Chief Police Officers (Acpo), Mr Grange held the organisation's personal crime portfolio and was its spokesman on child protection issues.
In that role he has given evidence to MPs on their inquiries into police investigations of institutional child abuse and Victoria Climbie, an eight-year-old who died of abuse and neglect.
He was also known for his tough line on illicit drugs.
In an interview with a local newspaper he was once reported to have said that all drug barons should be "put up against the wall and shot".