Yegor Gaidar was reportedly working on a book
Yegor Gaidar, the architect of Russia's market reforms in the 1990s, has died aged 53, his spokesman has said.
The spokesman said Mr Gaidar had died of a blood clot.
Mr Gaidar was Russia's acting prime minister in 1992, launching the "shock therapy" reforms after the collapse of the Soviet Union.
Mr Gaidar is credited with carrying out the first wave of privatisations under President Boris Yeltsin. His lifting of price controls was highly unpopular.
The policies angered millions of Russians who saw their savings devalued, while prices, which in some cases the government had kept artificially low for decades, suddenly rocketed.
Countless jobs were lost in bloated state industries as they struggled to adapt to new economic realities.
Perhaps because of that, Mr Gaidar's reforms are still remembered with loathing by many ordinary people, says the BBC's former Moscow correspondent James Rodgers.
But there is no question that he was a hugely influential figure, he adds.
In his mid-30s when Russia's then-President, Boris Yeltsin, made him acting prime minister, Mr Gaidar was never confirmed in his post.
A parliament which was still dominated by Soviet-era thinking refused to approve his candidacy.
However, his supporters argue that his reforms made Russia's later economic boom possible.
His contemporaries on the liberal wing of Russian politics in the 1990s praise him for taking difficult decisions which, they believe, saved the Russian economy from total disaster.
Former Soviet President Mikhail Gorbachev, who opposed Mr Gaidar's reforms, said he was personally grieving for his death, but that his policies had faults.
June-Dec 1992: Russian acting prime minister
Implemented economic "shock therapy"
Director of Institute for the Economy in Transition
"Gaidar went into politics with many hopes but his plan was to [resolve all the problems] in one shot," Mr Gorbachev said, according to Itar-Tass news agency.
Fellow reformer and former Deputy Prime Minister Anatoly Chubais wrote on his website: "Russia was tremendously lucky that Gaidar was there in one of the hardest moments of its history.
"At the beginning of the 1990s, he saved the country from hunger, civil war and collapse."
Lord Richard Layard, a British economist who worked closely with Mr Gaidar during the period of reform, said he was saddened when he heard the news.
"When I was working with him, he was in his mid-30s, which was an extraordinary thing for someone of that age to be doing - to introduce a market economy into Russia," he said.
"He was a giant figure and after he fell from power, he behaved with extraordinary dignity in Russia. He was still consulted by presidents and respected very much and it is a tragedy that he has gone."
Mr Gaidar later headed a Moscow-based think tank which had criticised then-President Vladimir Putin's economic policies.
However, Mr Gaidar was widely seen as a marginal political figure in recent years.
Three years ago he collapsed while on a book promotion tour in Ireland - a day after former Russian KGB agent Alexander Litvinenko died of radioactive poisoning in a London hospital.
Mr Gaidar's symptoms also suggested poisoning, but this was never confirmed. He blamed enemies in the Kremlin.