The following are details on the four jailed spies President Dmitry Medvedev pardoned with a special decree as part of Cold War-style spy swap that would involve the exchange of 14 agents.
A nuclear expert and former research fellow at the Moscow-based Institute for U.S. and Canadian Studies, Sutyagin was sentenced to 15 years in jail in 2004.
He was charged with passing classified military information to a British firm which prosecutors said was a front for the U.S. Central Intelligence Agency. He has always said he was innocent.
His lawyer, Anna Stavitskaya, said he had been told by Russian officials that he would be swapped in Vienna.
Sutyagin's brother, Dmitry, said by telephone on Friday that it was still unclear whether the swap had taken place and that he was waiting for a call from his brother.
Skripal, a former colonel of Russia's military intelligence, known as GRU, was convicted in 2006 on charges of espionage for Britain's MI6 intelligence agency. He is currently serving a 13-year prison term.
At the time of his conviction, Russian media said he had exposed dozens of Russian intelligence officers operating for Britain's MI6.
Former colonel in Russia's Foreign Intelligence Service known as the SVR, Zaporozhsky was convicted in 2003 and sentenced to 18 years in prison on charges of treason.
At the time, Russian media speculated that Zaporozhsky had been behind the exposure of former FBI agent Robert Hanssen and ex-CIA officer Aldrich Ames, both convicted on charges of spying for Russia.
Upon retirement in 1997, Zaporozhsky moved to the United States, where he was suspected to have shared classified information with intelligence agencies there. He was arrested upon returning to Russia in 2001.
Vasilenko, a KGB recruiter who worked in Washington in the 1970s and 1980s, was arrested in 1988 in Havana and spirited back to Moscow by the Soviet intelligence services. He was charged with espionage for the West and jailed.
Some former spies have said Vasilenko was wrongly fingered by Soviet mole Hanssen.
In 2005, another Gennady Vasilenko appears but it was impossible to confirm if this was the same Vasilenko who was arrested in Havana.
This Gennady Vasilenko, a former spy and deputy head of the security department at NTV-Plus satellite TV channel, was jailed for the illegal possession of arms, planting explosives and resistance to arrest. No charges of espionage were brought against him.