image captionGeorge Blake told the BBC he had betrayed more than 500 Western agents to the Soviet Union - PA MEDIA
Over nine years, the Soviet spy handed over information that led to the betrayal of at least 40 MI6 agents in Eastern Europe.
He was jailed in London in 1960, but escaped in 1966 and fled to Russia.
The Russian Foreign Intelligence Service said Blake "had a genuine love for our country".
Russian president Vladimir Putin described him as an "outstanding professional of special courage and life endurance".
"Throughout the years of his hard and strenuous efforts he made a truly invaluable contribution to ensuring the strategic parity and the preservation of peace on the planet," he said in a message of condolence.
"Our hearts will always cherish the warm memory of this legendary man."
His father was a Spanish Jew who had fought with the British army during World War One and acquired British citizenship.
In an interview with the BBC in 1990, Blake said he estimated that he betrayed more than 500 Western agents but he denied suggestions that 42 of them had lost their lives as a result of his actions.
His downfall came when a Polish secret service officer, Michael Goleniewski, defected to the West, bringing his mistress and details of a Soviet mole in British intelligence.
Blake was recalled to London and arrested. At a subsequent trial he pleaded guilty to five counts of passing information to the Soviet Union.
Analysis by Gordon Corera Security correspondent
George Blake did enormous damage to British intelligence operations during the Cold War, betraying agents and secret operations and showing that the KGB could run agents within the heart of the British state.
His escape from prison added to the embarrassment.
The reasons behind Blake's actions sometimes seemed mysterious, particularly his initial recruitment.
When I contacted him a decade ago, he told me: "It is no longer of particular importance to me whether my motivations are generally understood or not."
Part of the problem for him was that he had chosen communism but lived to see its collapse and the end of the Soviet Union, living out his days in Russia, where he was still seen as a hero by the successors to the KGB.
In 1995, Blake's escape from HMP Wormwood Scrubs became the focus of the play Cell Mates, starring Stephen Fry and Rik Mayall.
And in 2015, the BBC documentary Masterspy of Moscow followed what it called "the strange life" of an "enigmatic traitor".