Alexander Yakovlev - seen as a key figure behind Mikhail Gorbachev's perestroika reform policies in the former USSR - has died aged 81.
Yakovlev was in charge of ideology in the Politburo in the 1980s
Yakovlev joined the Communist Party's ruling Politburo in the mid-1980s, spearheading Gorbachev's drive for more openness and press freedom.
He also played a key role in efforts to expose past crimes under Soviet rule.
Yakovlev died in Moscow after a protracted severe illness, Russian media report.
"Yakovlev's death is a huge loss for all those who linked their lives with the struggle for freedom and democracy," Mr Gorbachev was quoted by Russian news agency Interfax as saying.
Vladimir Pekhtin, a senior member of pro-Kremlin party United Russia, said a whole era of struggle to build a civil society had passed with his death.
Was Alexander Yakovlev the real force behind perestroika and glasnost?
This debate is now closed. Thank you for your comments.
For all the openness and democratisation of the Gorbachev era, the enduring impact on the society of the former Soviet Union can hardly be described as positive. Almost all of the former Soviet republics are now engaged in some sort of civil war; living standards have plummeted with an immense human cost running to millions of lives (15 million according to the United Nations); and even those democratic freedoms that were won have all but disappeared. It is important to distinguish between glasnost and perestroika. Perestroika, which Yakovlev was most closely associated with, was more about free market reforms and privatisation than about openness and democratic rights. The social impact of perestroika - which continues to this day - has been overwhelmingly negative.
Paul Levy, Aarhus, Denmark
As an avid follower of events in those heady days of Perestroika and Glasnost, I am saddened to hear of the passing of this fine man. Indeed, he is the second of the two great - but unrelated - Yakovlevs - of the Gorbachev era to have passed away in less than a month. Just a couple of weeks ago, we heard of the demise of Yegor Yakovlev, the courageous editor of Moscow News, a must-read in those days for its scoops and new revelations about the 'blank spaces' in Soviet history. Now we mourn the passing of the intellectual brains behind the USSR's democratisation within the upper echelons of the Party apparatus itself. At a time when the lights seem to have gone out on Russia's democratic awakening under Putin's authoritarian machine, there is a certain poignancy in hearing about the death of these two great men within weeks of each other. Vive Gorbachev!
Fiona, Paris, France
Rest in peace friend. As one of the key architects in the plan that brought us freedom you will always be in our hearts.
Mihai Tudor, Hermanstadt, Romania
The passing of Alexander Yakolev should be mourned by all. As a champion of intellectual honesty, architect of the changes that ultimately brought down the USSR, he remained an outspoken beacon of moderation, and the democratic political process in Russia. We all owe him a measure of thanks for his positive historical role in the peaceful collapse of the world's last empire.
Paul Joyal, Washington, DC, USA
Yakovlev's impact on modern history cannot be underestimated. Unfortunately, his impact is far from being inspirational. He is responsible for releasing freedom in a destructive way. As a result of his thought leadership, not only the country (Soviet Union) broke up, but also the economy and political stability in virtually every country in the former Soviet space were crippled. Yakovlev's failure to think as a transition manager is as phenomenal as his success in providing ideological leadership in the adverse political setting of the Soviet Union. In short, Yakovlev has affected the course of modern history but his impact is controversial.
Yevgeni Garif, Moscow, Russia
When I was 6-years-old, my mother and I fled Communist Czechoslovakia to escape the oppression in our country. We were not allowed to travel back for visits and I thought I could never set foot in my country again. From bitter experience in 1968, when the Soviet Union crushed an attempt at democratic reforms in Czechoslovakia, Czechs knew that without Russia's consent, we would never have freedom. Without Yakovlev and Gorbachev, there would be no freedom in Eastern Europe today. RIP Alexander.
It would be difficult to overestimate Yakovlev's role in pushing glasnost forward. I was fortunate enough to interview him in 1994, when making a radio series for World Service to mark ten years of Gorbachev coming to power. He was not typical for a Politburo member; as well as understanding better than most of his colleagues what "freedom" meant, he also had a keen sense of humour. I remember him with affection and great respect.
Stephen Dalziel, London, UK
It is with great sadness that I read about Alexander's death. We met when I was with the Foreign Office in the 1980s and he rather than Gorbachev was the real engine of change in the USSR. Incidentally 'Sandy' - as I affectionately knew him - took an interest in Scottish football and supported Queen of the South. He just loved the irony of that name. RIP Sandy.
Bill Stitt, Edinburgh
Being a teenager in Western Europe when the Berlin wall came down, we all saw perestroika and glasnost as God sent. At that time Michael Gorbachev was mostly what we heard about. But, we knew there were many more "risking their lives" to bring this about. I am happy that you now mentioned one more of these people.