What do we know about the Russian military intelligence unit suspected by Britain of being behind the Salisbury Novichok attack?
The GRU – The "Main Directorate of Intelligence" of Russia – was founded in 1918 after the Bolshevik Revolution of Lenin.
Lenin insisted on his independence from other secret services and GRU was seen as a rival by other Soviet secret services, like the KGB.
Before the Russian Federation came into existence, the unit was subordinated to the most famous and feared KGB, the notorious internal security service of the Soviet Union.
The GRU – Main Directorate of Intelligence of Russia – was founded in 1918 after the Bolshevik Revolution of Lenin. Russian President Vladimir Putin is seen above, on the left, with then Defense Minister Sergei Ivanov on the roof of the new GRU headquarters in 2006.
GRU, one of whose divisions has an emblem with a bat suspended over a globe, was founded as the Registration Authority in 1918 after the Bolshevik Revolution
The FSB eventually succeeded the KGB, the Federal Security Service of the Russian Federation.
Vladimir Putin was a member of the KGB for 16 years and later briefly the head of the FSB.
According to Yuri Shvets, a former KGB agent, the GRU officers were referred to as "hard" but unsophisticated boots.
"The GRU took its officers out of the trenches," he said, while the KGB chose its agents from the best universities in the USSR.
The GRU – an acronym for Glavnoye razvedyvatel & noke upravleniye – would train agents and then send them to represent the Soviet Union abroad as military attachés in foreign embassies, according to the historian John Barron.
But once he is a member of the GRU, it is believed that it is exceptionally difficult to leave. And those who do it to join foreign agencies were savagely punished.
Viktor Suvorov, a GRU officer who defected to Britain in 1978, said the new recruits were shown a video of a traitor from the agency who was burned alive in a furnace as a warning.
Before the Russian Federation came into existence, the unit was subordinated to the most well-known and feared KGB, the notorious internal security service of the Soviet Union. The headquarters of GRU is seen above in Moscow
In recent years, the agency has gained notoriety for its connection to some of Russia's most controversial actions abroad.
In July of this year, United States Special Advisor Robert Mueller formally charged 12 GRU officers, accusing them of interfering in the 2016 presidential election in the United States.
The Bellingcat research team has linked the demolition of MH17 in eastern Ukraine in 2014 with a GRU official who said he "oversaw the acquisition and transport of weapons".
The agency has also been linked to an attempt to overthrow the government of Montenegro on the eve of the October 2016 parliamentary elections.
The GRU is now considered Russia's largest foreign intelligence service, according to Reuters, dwarfing Moscow's best-known Foreign Intelligence Service (SVR), which is the successor to the KGB's first CEO.
Unlike the KGB, the GRU did not split when the Soviet Union collapsed in 1991.
It has a special status and responds directly to the chief of staff, one of the three people who control Russia's portable nuclear control system.
The bosses of GRU are elected by Putin himself.
Russian military intelligence has a network of espionage abroad that experts in espionage believe is several times larger than that of the Foreign Intelligence Service of Russia.
Its experts decipher and analyze espionage information compiled by dozens of Russian military military satellites.
It also has several elite units of special forces that fought in many post-1945 conflicts, including Afghanistan, Chechnya and the Syrian Civil War.
In 1997, it was thought that it controlled 25,000 special forces troops.
Russian President Vladimir Putin and Sergei Ivanov observe the emblem of the Spetsnaz of the GRU, or special forces
The GRU confirmed or tacitly accepted that it was behind some of the main espionage operations abroad. He has also been accused of many operations that he denies.
Former FSB agent Alexander Litvenenko – who was killed in London by Russian intelligence after defecting in Britain – was one of many Russians who accused the GRU of being involved in four attacks on apartments in Moscow in 1999.
He alleged that it was a successful coup designed for Putin, who was then prime minister, to be elected president after he launched a popular invasion of Chechnya in revenge for the bombings.
Western governments and intelligence agencies also believe that GRU is behind the piracy groups Fancy Bear and Guccifer 2.0.
It is believed that Fancy Bear was responsible for attacks against official organizations within the NATO states, including the German parliament.
He is also accused of interfering in the French elections of 2017 and in the International Olympic Committee among other global institutions.
The GRU, however, has also suffered several humiliating blows to its reputation after some of its main agents defected to the west.
Spetsnaz soldiers from the Russian Interior Ministry patrol the grounds around the Beslan airport in the Russian republic of North Ossetia in this archive photo. GRU also has several elite units of special forces that fought in many conflicts, including Afghanistan and Chechnya
One of those deserters was Oleg Penkovsky, a friend of the then head of GRU. He informed Washington of a Moscow operation to place nuclear missiles in Cuba.
The scandal led to the crisis of Cuban missiles and the world on the verge of a full-fledged nuclear war for several days.
Penkovsky was arrested in 1962 and executed in 1963 after being convicted of high treason and espionage.
Sergei Skripal, a former colonel at GRU, was considered by the Kremlin to be one of the most damaging spies of his generation.
He was responsible for unmasking dozens of secret agents that threatened Western interests operating undercover in Europe.
Col Skripal, 66, allegedly received £ 78,000 in exchange for taking big risks to pass classified information to MI6.
In 2006, he was sentenced to 13 years in a Russian labor camp after being convicted of passing invaluable Russian secrets to the United Kingdom.
An important source in Moscow said at the time: & # 39; This man is a great hero for MI6 & # 39;
After being convicted of "high treason in the form of espionage" by the Moscow military court, Col Skripal was stripped of his rank, medals and state awards.
The Russian security service, the FSB, accused him of having started working for the British secret services while serving in the army in the 1990s.
He passed information classified as state secrets and MI6 paid him for the work, the FSB said.
Col Skripal pleaded guilty in the trial and cooperated with the investigators, reports reported at the time. He admitted his activities and gave a complete account of his espionage, which led to a reduced sentence.
In July 2010, he was pardoned by then Russian President Dmitry Medvedev and was one of four spies exchanged by ten Russian agents deported from the US. UU In a historical exchange that involved the redhead & # 39; femme fatale & # 39; Anna Chapman
After the exchange at the Vienna airport, Col Skripal was one of the two spies who arrived in Britain and has maintained a low profile for the past eight years.
The former spy was living in one direction in Salisbury, Wiltshire, when suspicion of poisoning took place in the center of the city.