A Soviet spy who died this week is said to have changed the course of history when she helped spoil a Nazi assassination plot — but you've probably never heard her name.

Key points: Goar Vartanyan died aged 93, seven years after husband and fellow spy Gevork

Goar Vartanyan died aged 93, seven years after husband and fellow spy Gevork The Vartanyans were instrumental in shutting down a plot to assassinate the "Big Three" leaders in WWII

The Vartanyans were instrumental in shutting down a plot to assassinate the "Big Three" leaders in WWII The foiled operation inspired a movie and a number of books

Goar Vartanyan died on Monday aged 93, leaving a legacy of history-defining secret agent work during the WWII era and beyond.

It is understood she will be buried alongside her husband, Gevork Vartanyan, also a secret agent and one of Russia's most decorated spies, who died seven years ago.

Russian President Vladimir Putin said Ms Vartanyan and her husband devoted their lives to serving their country.

An undated photo of the couple, supplied to Russia Beyond from a personal archive. ( Supplied: Russia Beyond/Unknown )

How the history-defining moment unfolded

One of Ms Vartanyan's most famous and influential missions was in 1943, at the Tehran Conference attended by Franklin Roosevelt, Winston Churchill, and Joseph Stalin.

The "big three" allied leaders of the era travelled to Iran's capital for the meeting, which took place from November 28 to December 1, to discuss the logistics of an impending invasion on German-occupied France in the midst of World War II.

But there was a deadly plot in the works.

"Operation Long Jump" was launched by a group of Nazis to assassinate Stalin, Churchill and Roosevelt at the conference, with the plan allegedly backed by Adolf Hitler himself.

"The Big Three" world leaders during World War II, Joseph Stalin, Franklin D Roosevelt and Winston Churchill. ( Supplied: Getty )

Gevork Vartanyan and Goar were both agents at the time, Gevork aged 19 and Goar just 16.

In an interview on American cable show Spotlight decades later, not long before his death, Mr Vartanyan said he did not know if the leaders were aware they were in danger ahead of the conference.

"First of all they (Nazis) thought maybe they (could) succeed in kidnapping. If not they'd just kill them," he said in the interview.

"I had a group of seven young people like me, about 17, 18 years old at that time."

The Germans had come up with a plot to kill the leaders at the 1943 Tehran Conference. ( Supplied: Lt D. C. Oulds/Imperial War Museums )

Gevork told interviewer Al Gurnov that the group of teen spies discovered German parachutes dropping near where the conference was to be held, and tapped into radio frequencies to gain intelligence on the operation.

The operation was foiled by the group, including Goar and Gevork Vartanyan, and the suspects arrested before any assassination attempt could be carried out.

The conference went ahead and the "big three" survived - and the rest is history.

Soviet film Teheran 43, released in the early 1980s, was inspired by the fascinating story, as were a number of books.

A movie poster for the Soviet film Teheran 43, inspired by true events. ( Supplied: Mosfilm )

What led to life as a spy

Goar Vartanyan was born in 1926, and in her teens moved to Iran and joined an anti-fascist group led by Gevork Vartanyan.

This was the beginning of what would become a fascinating career in undercover operations for the Soviet Union.

The couple had distinguished careers as spies for decades, and Ms Vartanyan continued to train young secret agents even after her retirement in 1986.

Gevork Vartanyan died in 2012 at age 87. He was bestowed the title of Russia's highest honour, Hero of the Soviet Union, and Russian President Vladimir Putin attended his burial ceremony.

Ex-Soviet spy couple Goar and Gevork Vartanyan. ( Supplied: Islamic Republic News Agency/original source unknown )

A spokesman for Russia's Foreign Intelligence Service told AFP that Ms Vartanyan would be buried at Troyekurovskoe Cemetery in Moscow, the same cemetery as her husband.

There is still plenty of mystery surrounding the full impact the couple had on national security and undercover operations throughout their careers, with local media reporting that much of their work will remain classified even after their deaths.

A distinguished career recognised

Russia's Foreign Intelligence Service announced Ms Vartanyan's death on Monday, describing her as a heroine.

"Together with her husband... they were one of our most beautiful, charming and at the same time productive couples among our intelligence illegals," Foreign Intelligence Service chief Sergei Naryshkin said.

Mr Putin sent a message of condolences to the director of the Foreign Intelligence Service of Russia and its employees yesterday, and said Goar and Gevork Vartanyan were an iconic agent couple of the Soviet intelligence service.

"Goar Vartanyan belonged to a galaxy of brilliant professionals who devoted their lives to serving their homeland," the message read.

Russian President Vladimir Putin pictured with Goar Vartanyan on International Women's Day in the Kremlin in 2005. ( Reuters/Itar Tass/Kremlin Press Service )

"Together with her husband, Gevork Vartanyan, she made a truly unique contribution to strengthening our national security. They added striking, heroic pages to the history of Russian foreign intelligence.

"The memory of Goar Vartanyan — a wonderful person and genuine patriot — will always live on in the hearts of her family, colleagues and friends."

Putin's press secretary, Dmitry Peskov, also made a statement yesterday expressing condolences to the Vartanyan family and said Mr Putin knew the couple well.

"Without Goar Vartanyan and her husband Gevork, the history of our world could have been different," he told local media.

"These are people who left their mark on the history of mankind."

Mr Putin had met with the couple a number of times. ( Supplied: Islamic Republic News Agency/original source unknown )

Changing perspective of Russian spies

While the Vartanyans have been openly celebrated for their achievements, more recent media attention directed at Russian intelligence agencies has been less positive.

While he rarely participated in interviews, Gevork Vartanyan voiced his opinion on a "blow" to Russian foreign intelligence's image to a Bulgarian newspaper after a group of spies were arrested and deported from the United States, with social media use and language barriers revealing their identities.

"The self-promotion that they created on the internet looks unprofessional to me," he told Trud in 2011.

"The fact that people from the espionage profession allowed such things to happen is very strange."

Highly publicised incidents of an ex-spy and his daughter being poisoned and allegations of interference with doomed flight MH17 have affected Russia's Foreign Intelligence Service in recent years.

Reuters/ABC