George Blake, the former MI6 officer and one of the Cold War's most infamous double agents, has died aged 98, Russian media has reported.
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".
His death, reported by Russia's state-owned news agency RIA Novosti, was confirmed by Sergei Ivanov, the head of the press bureau of the Russian Foreign Intelligence Service (SVR).
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."
