BBC security correspondent
Mr Evans: Taking over at challening time
Jonathan Evans will take over one of the most intense and pressured roles in government next month when he becomes director general of the Security Service, commonly known as MI5.
Evans was the front-runner for the job and since 2005 had occupied the position of deputy director general, traditionally the position in which successors for the top job are groomed.
The director general is accountable to the home secretary and prime minister for all MI5 operations.
He will be the 16th director general since the service was founded in 1909.
Many were former military officers and diplomats, although in recent years the trend has been to appoint from within.
Until 1993 the name of the head of MI5 was not made public.
The career of Mr Evans has closely tracked the evolution of MI5 from the old days of the Cold War to the new world of international terrorism.
Evans joined MI5 in 1980 after graduating with a degree in classical studies from Bristol University.
MI5, based in London, has had to evolve since the Cold War
At that time the main task of MI5 - as it had been since the start of Cold War - was monitoring the work of the Soviet Union and communists inside the UK.
Evans began his career in the field of counter-espionage investigations; the hunting of spies and moles.
In 1985 he moved to work in protective security, advising departmental security officers on the protection of classified information.
With the end of the Cold War, MI5 like other intelligence agencies was plunged into something of an identity crisis.
It began to focus more on organised crime and also engaged in a bureaucratic tussle with the police to take charge of counter-terrorism in Northern Ireland.
This proved deeply controversial for all agencies involved because of allegations of collusion with paramilitary groups in the campaign against the IRA.
Mr Evans worked closely on Northern Ireland in the late 1980s and 1990s.
He also worked as head of MI5's secretariat and spent two years attached to the Home Office where he was closely involved in the development and implementation of VIP security policy.
From 1999 onwards, Evans became directly involved in countering the threat from international terrorism.
In 2001 he was appointed to the Security Service's Management Board as director of international counter terrorism - ten days before the 9/11 attacks on the World Trade Centre.
Pressure on MI5
The 9/11 attacks began a process of massive change for MI5 which gathered pace over the coming years.
only 23% of its operational effort was directed against the Islamist terrorist threat but by July 2005 this had risen to 56%.
Outgoing head Eliza Manningham-Buller said MI5 was at full stretch
The organisation is set to double in size by 2008, although a recent parliamentary oversight report argued that more could have been done faster in terms of bringing Britain's counter-terrorism capabilities up to speed.
But insiders say there is a limit to the speed at which an organisation can grow and train new people in such a sensitive area.
In April 2005 Dame Eliza Manningham-Buller told the home secretary she intended to resign two years later and Mr Evans was appointed deputy director general later that year.
It was in July of that same year that the first successful al-Qaeda attack against the UK was launched.
The aftermath of that attack led to a number of questions about whether MI5 had missed any of the bombers as well as growing public interest and questioning about the organisation and its work.
The days in which MI5 worked in the shadows are long gone due to the nature of the terrorist threat and way it impacts on people's lives as well as the political debate surrounding the subject.
This has led to the organisation slowly becoming more open, for instance launching its own website and the director general making occasional speeches.
In one of those speeches in November 2006, Dame Eliza Manningham-Buller made clear that her successor would be inheriting an organisation at full stretch.
She warned that MI5 was watching 200 networks comprising over 1,600 individuals and that it was witnessing close to 30 potential mass casualty plots in development.
She warned that the hard choices involved in the work of MI5 were always going to involve risk, something Evans will be more than aware of as he steps, at least partially, into the spotlight.