She was widely credited as the model for Judi Dench’s M in the James Bond films - and it's clear to see why.
Under Dame Stella Rimington’s sterling leadership, M15 underwent a far-reaching transformation.
Joining MI5 in 1969, she became its first female head and the first to be publicly named.
She had a varied career including roles in counter-subversion, counter-espionage and counter-terrorism.
Dame Stella, who has died at the age of 90, was appointed director general of MI5 in 1992.
During her tenure there were threats from the IRA and Russia, while the Islamist terror threat was also emerging.
She oversaw MI5 taking lead responsibility for countering Irish republican terrorism in Great Britain and the move of MI5’s headquarters to Thames House.
She also instituted a policy of greater public openness to demystify the work of MI5 including beginning a programme of releasing MI5 files to The National Archives.
Speaking on BBC Radio 4's Woman's Hour in 1999, Dame Stella said she had "thoroughly approved" of the decision to make her name public when she became director general.
However, she added that she hadn't "really guessed quite how much interest there was going to be and the great level of press attention".
She said "very rapidly" she and her family had needed to move from their "ordinary London street" and "effectively go underground, which was a rather strange reverse when one had been trying to be more open".
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Dame Stella retired from MI5 in 1996 and was appointed Dame Commander of the Order of the Bath later that year.
Following the news of her death, current MI5 Director General Sir Ken McCallum offered his condolences on behalf of the entire organisation.
Paying tribute, he said his predecessor - as the first publicly stated female head of any intelligence agency in the world - "broke through long-standing barriers and was a visible example of the importance of diversity in leadership".
He added: “Her leadership ushered in a new era of openness and transparency about the work MI5 does to keep this country safe, a legacy that continues to this day.
“Our thoughts and deepest sympathies are with her husband, two daughters and extended family.”
Sir Richard Moore, head of MI6, said Dame Stella was a "true trailblazer".
After her retirement in 1996, she became a non-executive director of Marks & Spencer and the BG Group.
READ MORE: To read all obituaries and tributes join the Facebook group Norfolk's Loved & Lost
She later reinvented herself as a novelist from her home in mid-Norfolk, drawing on her own experience to bring her fictional spy stories to life.
While guest editing the Today programme in 2007, she said spy writers had created "a totally glamorous world around the profession of spying" that "bears very little relation to reality".
She wrote more than a dozen thriller books based on her Secret Service experience, and her autobiography, Open Secret, sparked controversy in 2001.
At the time, there were attempts to try and block publication over fears it could jeopardise the safety of secret service officers.
In 2014 she revealed on BBC Breakfast that her novels had to be submitted to the security service for clearance, and that she had occasionally been asked to change names and places by MI5.
Dame Stella was born on May 13, 1935 in South Norwood, in south London. She died on Sunday, August 3.
In a statement, her family said: “She died surrounded by her beloved family and dogs and determinedly held on to the life she loved until her last breath.”
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