At the Brandenburg Gate in Berlin this week, one of the defining figures of last century's history celebrated the 20th anniversary of the fall of the Berlin Wall, in which he played a key role.

Lech Walesa and Hillary Clinton, invited to listen to Daniel Barenboim conduct the Staatskapelle Berlin, were in the audience.

But the star guest was undoubtedly Mikhail Gorbachev, the former Soviet premier under whose leadership the Cold War in eastern and central Europe was brought to an end.

If a sense of his importance to the events of 1989 is required, it was supplied by British historian Timothy Garton Ash, who described Gorbachev's "breathtaking renunciation of the use of force" while Soviet leader as "a luminous example of the importance of the individual in history".

Garton Ash's reminder feels long overdue. For there is a conundrum concerning Gorbachev: it is why a living figure of such historic moment appears to have receded so far in our memory in comparison with contemporaries such as Nelson Mandela or Ronald Reagan.

Is it, perhaps, because his momentous experiment ended so inauspiciously with a failed coup, the implosion of the Soviet Union on a wave of nationalist sentiment in the republics and Russia itself, and a resignation that effectively finished his political career?

These events preceded the rise of a voraciously destructive klepto-politics in Russia, so venal that people would come to yearn for the certainties even of Stalin's rule.

Or is it because the world has judged that he has diminished himself with the album of traditional ballads, the adverts for Pizza Hut and Louis Vuitton, the speaking tours and celebrity galas, the cameo film role in a Wim Wenders film playing - inevitably - himself? Stage antics of an old gunslinger trading on fading memory.

The truth is that Gorbachev meant, and means, more than that.

Not the Gorbachev of now, but the "Gorby" of then: architect of glasnost (openness) and perestroika (economic restructuring) - two Russian words that for a while seemed in every news bulletin. The builder of bridges with the West, renouncer of the Stalinist notions of the use of force who, through his actions and inactions, changed the world. The man with whom Margaret Thatcher and Ronald Reagan could do business.

For while what he attempted for the Soviet Union has crumbled, what has survived has been the legacy of that remarkable year two decades ago when eastern and central Europe were plunged into a series of largely bloodless revolutions against their Warsaw Pact leaders. And Gorbachev did not send in the tanks. But there was more to it than that. In many respects, he set the conditions for that year of revolutions, leaving a question to persist: whether it was Gorbachev himself or a harder to define "Gorbachev effect" that was more significant in influencing the transformations that shook Europe.

Born in Privolnoye, near Stavropol in 1931, Gorbachev's was a remarkable rise. Driving combine harvesters in his teens, he went on to read law at Moscow State University where he met his wife, Raisa. The years that would follow, after he joined the Communist Party, were marked by a precocious advance: youngest of the provincial party chiefs; youngest member of the ruling politburo, much of it under the patronage of Mikhail Suslov, chief party ideologue. Despite his conservative outlook, Suslov would inform the development of Gorbachev's later ideas, opposing force except in what he regarded as a last resort - although that definition included the crushing of the Prague Spring in 1968.