Alexander Yakovlev, who has died in Moscow aged 81, was the most powerful - and most contradictory - intellectual in the top echelons of the Soviet Communist party in its final decade. A one-time academic, diplomat and ideologue, he provided the theoretical backing for Mikhail Gorbachev's perestroika (restructuring), and then turned fiercely not only against Bolshevism but Marxism itself, calling it a philosophy concerned only about "the misfortune of the idler, not the worker". After the collapse of the Soviet Union he briefly attempted to form a "party of the middle class", before settling on a retirement career of polemical writing.
Born in the village of Korolevo, near the Volga, to parents who were barely literate, Yakovlev came to adulthood during the second world war. Like many young Russians, he joined the Communist party because of its role in organising resistance to the Nazi invasion. Called up in 1941, he was wounded in 1943 near Leningrad, and became a communist the following year. After the war, he moved to Moscow and studied at the party's academy of social sciences. Clever and undoubtedly faithful to party doctrine, he was allowed to spend a year in 1958-59 as an exchange student at Columbia University, New York.
On his return, he quickly climbed the ladder in the party's ideological apparatus and was, by 1965, acting head of the central committee propaganda department. In 1972 he published an article in the important weekly, Literaturnaya Gazeta, which criticised nationalism and chauvinism, including Russian nationalism, and upset senior figures.
He was sent to Canada as Soviet ambassador in what was seen as a kind of demotion. But it was in this job that he caught the eye of Gorbachev, who met him on a parliamentary trip to Ottawa in 1983 and arranged for him to return to Moscow as head of the prestigious think tank, IMEMO, the Institute of World Economy and International Relations. When Gorbachev became general secretary of the central committee in March 1985, Yakovlev was put in charge of ideology and two years later joined the politburo.
A short, plump, owlish figure, Yakovlev became the architect of Gorbachev's policy of non-intervention in eastern Europe, which was based on the hope that local communist parties could reform and liberalise (and even win multi-party elections). He championed the idea that universal human values should take precedence over class struggle, and that in the Soviet Union itself the Communist party should abandon its monopoly of power and accept the challenge of pluralism.
In 1989 he headed a commission set up to investigate Stalin's purges and rehabilitate victims. He was also in charge of the official examination of Stalin's non-aggression pact with Hitler, and the forced annexation of the Baltic states. Increasingly the target of conservatives, who hinted that his two sojourns in the west had compromised him, Yakovlev took the main brunt of the attack at the party's last congress in July 1990. He was assailed for "losing" eastern Europe and trying to introduce capitalism. While Boris Yeltsin resigned from the party during the congress, Yakovlev decided to remain, but angry delegates voted against his re-election to the central committee.
By then a member of the new, and more influential, presidential council, Yakovlev joined Eduard Shevardnadze, the liberal foreign minister, in urging Gorbachev not to give ground to conservatives calling for a clampdown on the "popular front" movements in the Baltics and other Soviet republics. In July 1991, he and Shevardnadze signed a manifesto for a Movement for Democratic Reforms, an attempt to split the Communist party in the hope that its more liberal members could head a broad coalition of party and other activists.
Yakovlev was gloomy about the prospects. On the eve of the 1991 attempted coup, he told me that although the "party has become shapeless", Russia's authoritarian traditions augured ill for reform. "Even now, many democratically-minded people are still hoping for a good tsar, but that's not the way to set up a democratic society," he said.
Yakovlev denounced Bolshevism for "its fixation on keeping power at any cost, by force and unconstitutional means, if necessary" - an argument he elaborated in retirement, when he made it clear that he favoured the February 1917 revolution (which overthrew the tsar), but not the October revolution later that year.
He rejected the reform under which workers could elect factory managers, which was briefly introduced in 1987. "Free elections should be confined to the political sphere, not the economic. In production you need discipline and one-person management," he insisted.
After the attempted coup, Yakovlev played a key role in persuading Gorbachev to disband the Communist party. With his loyalty torn after many friends switched towards Yeltsin, and convinced that Russia needed comprehensive market reforms, Yakovlev nevertheless stayed with Gorbachev until the collapse of the USSR in December 1991. With Yeltsin now the supreme power, Yakovlev gradually moved into his camp.
In October 1993, Yakovlev (unlike Gorbachev) supported Yeltsin's disastrous decision to use tanks against the Russian parliament building to oust MPs who opposed his decree to dissolve parliament and write a new constitution. Shortly afterwards, Yeltsin put Yakovlev in charge of the state-owned Ostankino television station. Yakovlev resigned from this position in March 1995, and eventually patched up his links with Gorbachev.
He devoted his later years to writing his memoirs and what became increasingly emotional diatribes against Marxism. He was not optimistic about Russia itself, suggesting the country might be better off with different people; "We shall overcome all our misfortunes if we can overcome ourselves," he wrote in one jeremiad.
He is survived by his wife, son and daughter.
· Alexander Nikolaevich Yakovlev, politician, born December 2 1923; died October 18 2005