More recently, Berezovsky has made headlines for costly legal battles that have dealt serious blows to his finances.
Last year, the Russian business magnate was ordered to pay 35 million pounds ($53.3 million) in legal costs to fellow Russian Roman Abramovich, the billionaire owner of Chelsea Football Club, after losing a multimillion-dollar legal battle against him.
Berezovsky had claimed that Abramovich cheated him out of his stakes in the oil group Sibneft, arguing that he blackmailed him into selling the stakes vastly beneath their true worth after he lost Putin's good graces.
But a judge threw out the case in August, ruling that Berezovsky was a dishonest and unreliable witness, and rejected Berezovsky's claims that he was threatened by Putin and Alexander Voloshin, a Putin ally, to coerce him to sell his Sibneft stake.
It also recently emerged that Berezovsky ran up legal bills totaling more than 250,000 pounds in just two months of a case against his former partner, Elena Gorbunova, with whom he had two children and who claimed the businessman owed her millions.
Earlier this week, The Times of London newspaper reported that Berezovsky was selling property — including an Andy Warhol portrait of the former Soviet Union leader Vladimir Lenin — to settle his debts and pay expenses owed to lawyers.
The Russian president's spokesman, Dmitry Peskov, said in a telephone interview on state television that Berezovsky had sent a letter to Putin about two months ago asking to be allowed to return to Russia. In the letter, Berezovsky acknowledged having made many mistakes, Peskov said.
Peskov said he did not know how Putin reacted to news of the death.
"But you can say that information about the death of someone, no matter who he was, cannot elicit positive emotions," the spokesman said.
AP writer Lynn Berry in Moscow contributed to this story.
Cassandra Vinograd can be reached at http://twitter.com/CassVinograd
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