MOSCOW, Russia: Ninety years after the birth of Andrei Sakharov, who died in 1989 as the Soviet empire crumbled, the Nobel prize winning dissident remains an uncomfortable memory for Russian authorities.

“There is a conspiracy of silence. The state prefers not to talk about him. Our state does not need people like Sakharov, who had the courage to criticize,” said the former dissident Lyudmila Alexeyeva.

Co-designer of the Soviet nuclear bomb, Sakharov devoted much of his life to scientific research before joining in open dissent against the communist government in the 1960s.

Sakharov first threw down the gauntlet against the regime in 1966 when he signed a collective letter against Stalin’s rehabilitation as the Soviet dictator’s spectre rose again under Brezhnev, following a short-lived liberal thaw during Khrushchev’s leadership.

Paradoxically, latest polls show that Stalin remains popular in Russia and history textbooks present the wartime leader, whose regime saw millions die in repressions and forced collectivisation, in a somewhat positive light.

In 1968 -- while the Cold War was in full swing -- Sakharov again defied Communist ideology and published in the West an article titled “Reflections on Progress, Peaceful Coexistence and Intellectual Freedom.”The text, circulated clandestinely in the Soviet Union, cost him his job at the Arzamas secret nuclear centre, where he had worked for 18 years.

In 1970, Sakharov co-founded the Committee for Human Rights and began a tireless defence of political prisoners, ethnic minorities and civil and religious freedoms that won him acclaim in the West, culminating in the 1975 Nobel Peace Prize.

In 1980, he was arrested for his criticism of the Soviet intervention in Afghanistan and then exiled, without trial, to Gorky, now Nizhny Novgorod, a provincial city closed to foreigners.

It was Mikhail Gorbachev’s perestroika campaign that made possible his return to Moscow in 1986.

In modern-day Russia, no official institution maintains the memory of Sakharov who would have turned 90 on Saturday, only NGOs such as Memorial rights group and Andrei Sakharov Foundation.

“He is a Nobel Prize (laureate), a great scientist, one can not ignore him.But his philosophy based on human rights is profoundly alien to ourauthorities,” said Memorial’s chairman Arseny Roginsky.

“Sakharov has none of the national and patriotic ideology that prevails today in Russia.” According to a survey by the opposition weekly New Times, young Russians know Sakharov chiefly as the father of the atomic bomb -- a fact highlighted in history textbooks -- but not for the rights campaigning that made him a global symbol of political dissidents in the Soviet Union.

More than 20 years after his death in 1989, there is still no monument to the historic figure in Moscow, where numerous statues of Lenin can still be seen in the streets and train and metro stations.

There is only a modest memorial sign at the building where he lived and a little frequented street named after him.

A conference dedicated to Sakharov will be held in Moscow on Friday and Saturday, attended by former dissidents and political figures.

The Czech and Swedish foreign ministers, Karel Schwarzenberg and Carl Bildt, will participate, but no Russian ministers are expected to join them.