Berezovsky had claimed to be the subject of assassination attempts, and there were conflicting reports Saturday about the circumstances of his death.
PHOTOS: Notable deaths of 2013
Thames Valley police would not directly identify him, but told the Associated Press that the death was being treated as unexplained.
Born in 1946 to a Jewish family in Moscow, Berezovsky earned a degree in mathematics and worked as an engineer and researcher until shortly before the breakup of the Soviet Union, when he set up a private car-trading company.
That endeavor brought him his first millions of dollars, and by 1995, he also ran a bank and helped found Russia’s main national television network.
The next year, he helped organize a group of the richest and most influential Russian oligarchs to back and finance President Boris Yeltsin’s election campaign, which resulted in a controversial runoff victory.
Yeltsin returned the favor, granting Berezovsky and other oligarchs lavish chunks of state property.
Berezovsky eventually had interests in or controlled the Sibneft oil company, two television networks, the largest Russian air travel company, newspapers, magazines, a radio station and a car firm. His wealth was said to run into the billions of dollars.
Berezovsky’s political career also flourished during the late 1990s, when he served as the deputy head of Russia’s Security Council and held the post of executive secretary of the CIS, a union of post-Soviet states. From 1999 to 2000, he was a member of the lower house of Russian parliament.
Berezovsky said he first met Putin in 1991 and that he assisted in promoting him to chief of the FSB, the domestic successor to the Soviet KGB. Seven years later, he allegedly masterminded the campaign for Putin to succeed the ailing Yeltsin as acting president. In late 1999 and early 2000, Berezovsky conducted an unprecedented media campaign to help Putin win the presidential election.
“Berezovsky had an extremely brilliant mind of a mathematician and he also was a genius of political schemes and intrigues, but he grossly miscalculated Putin, which became his fatal mistake and largely served his ultimate undoing,” said Sergei Markov, a member of the Public Chamber, a Kremlin advisory body, and a staunch supporter of Putin.
Shortly after Putin came to power, he distanced himself from most of Yeltsin’s favorite oligarchs and demanded that they return major television companies to the state and pay full taxes on revenues from their oil businesses.
“Those who tried to oppose were thrown out of favor, including Boris Berezovsky, Mikhail Khodorkovsky and Vladimir Gusinsky,” Markov said.
Khodorkovsky is now in prison and Gusinsky is in exile in Spain.
Berezovsky had lived in Britain since 2003 and had been sought by Russian authorities, who said they suspected him of embezzling $47 million and conspiring to bring down the constitutional structure of the Russian Federation.
Over the years, Berezovsky conducted an active campaign to discredit Putin, including accusing the Kremlin of having organized explosions at residences in Moscow and two other cities, which resulted in hundreds of deaths and led to the war with Chechnya that helped consolidate Putin’s grip on power.
Last year, Berezovsky begged the public to forgive him for helping elevate Putin to the presidency.