Killing Eve's Villanelle was inspired by a real Spanish hitwoman who murdered 23 people in a series of shootings and car bombings.
Like Villanelle and 'the 12', Idoia López Riaño was recruited at a young age and went on to leave a bloody trail across Spain on behalf of Basque separatist group ETA.
Riaño, who earned the nickname La Tigresa, was known to prowl bars and seduce police officers in order to gather intel before killing their colleagues.
The creator of Villanelle - portrayed by Jodie Comer in the TV adaptation - is novelist and journalist Luke Jennings.
Advert
Jennings told LADbible: "I was researching women who kill for a cause - terrorists as opposed to domestic murderers of the Myra Hindley kind.
"She [Riaño] was quite interesting just because she was such a prolific killer."
In what sounds like a deleted scene from Killing Eve, one victim only survived an assassination attempt because Riaño - like Villanelle - reportedly enjoyed high fashion and got distracted by her own reflection in a shop window.
Jennings said: "The interesting thing to me is not so much that it was a fashion shop window but that she should be so narcissistic as to be drawn away from this very serious business just by her own reflection - this inability to distinguish between the trivial and the important.
Advert
"They're considering taking somebody's life and in the course of this process she just gets distracted by her own reflection - that is a deeply sociopathic piece of behaviour to say the least."
Introduced to ETA by a teenage boyfriend, Riaño quickly rose through the ranks during the group's bloodiest era.
One of Riaño's most devastating acts was her part in the 14 July 1986 bombing of Madrid's Plaza República Dominicana.
A vehicle loaded with 35 kilos of explosives and shrapnel was used to kill 12 Guardia Civil officers and left dozens more injured.
While there's nothing glamorous about La Tigresa's career as a killer, Villanelle has somehow managed to become the nation's favourite on-screen psychopath with the BBC's high-wire imagining of Jennings' books.
Advert
Jennings told LADbible: "This was a real person and she devastated countless people's families.
"I don't want to kind of trivialise her actions and just say that I based a fictional character on her but it was confirmation for me that sociopathic women are prepared to kill in this very promiscuous way.
"Is Villanelle a psychopath? Yes she is. I did quite a lot of research on the actual behaviour of psychopaths, but she is also a fictional character who I wanted people to engage with rather than just be horrified by.
"In reality, psychopaths - and I've met one or two - are just deeply unpleasant people."
Advert
Riaño was arrested in France in 1994 before being expedited to her home country of Spain.
She served a 23-year sentence and was released in 2017 as part of a deal which saw her condemn ETA's violence in a letter to Spain's national court.
Jodie Comer's portrayal of Jennings' character has seen her stun a global audience with her ability to hop between accents as her character stalks her prey around Europe.
Jennings said of the actor: "I thought she was exactly right. She had imagined the character very fully in her mind at a very early stage.
Advert
"She understood the character right from the start, and she had nailed the accent; that rather stateless Russian, French, English chameleon accent that the character has."
With the third novel, Killing Eve: Die for Me, recently released in paperback - and a fourth season of the TV show confirmed - the appetite for a character like Villanelle is greater than ever. But why are people so hooked on the story of a predatory assassin?
Jennings told LADbible: "I think people are fascinated by the question of what makes some people kill when most of us don't.
"People ask themselves the question, could I do this? Could someone I know do this? Could I be a victim of this?
"Deep questions about the nature of the human animal - how far are we from predators? What is civilisation?
"I think murder is when civilisation stops working. There's nothing more counter-civilised than murder really, is there?"
Killing Eve: Die for Me, the third book of the trilogy, is available in paperback here.
Topics: True Crime, News, Killing Eve