Boris Berezovsky, who has died in London aged 67, was a former Kremlin insider who bitterly fell out with Russian President Vladimir Putin.
The tycoon, whose death has been described by London police as 'unexplained", lost a $4.7bn damages claim in 2012 court case in London against fellow oligarch, Chelsea Football Club owner Roman Abramovich.
He was also a close friend of poisoned former KGB agent Alexander Litvinenko and was later accused of being behind his murder by Scotland Yard's prime suspect, Andre Lugovoi.
Born on January 23, 1946, in Moscow, the mathematician-turned-Mercedes dealer amassed his wealth during Russia's chaotic privatisation of state assets in the early 1990s after the collapse of the Soviet Union.
He gained political clout and opportunities to buy state assets at knockdown prices in return for backing the then-Russian President Boris Yeltsin.
Berezovsky made a fortune in oil and cars.
Yeltsin named Berezovsky deputy head of the powerful Security Council and chief negotiator with Chechnya shortly after it won independence from Moscow in a brutal war.
Berezovsky narrowly escaped an assassination attempt that decapitated his driver in 1995.
He went on to play a key role in brokering the rise of Yeltsin's successor, Putin, in 2000.
Putin effectively made a pact when he first became the Russian president: the oligarchs could keep their money if they did not challenge him politically. Those who refused often found themselves in dire circumstances.
Berezovsky later fell out of favour with Putin and fled into exile in November 2000, just in time to escape arrest on fraud charges.
The UK granted him political asylum in the UK in 2003.
He became the Kremlin's greatest nemesis in London, mockingly defying years of attempts to extradite him.
Berezovsky emerged from an extradition hearing in 2003 wearing a Putin mask. He told journalists: "Call me Vladimir Vladimirovich."
The Kremlin later accused him of planning a violent coup to overthrow Putin and his government.
He allied himself in the UK with an array of other Kremlin critics. Among them was Litvinenko, who fled Russia with Berezovsky's help after accusing officials there of plotting to assassinate political opponents.
Litvinenko accused the Kremlin from his deathbed in 2006, of orchestrating his poisoning from the rare radioactive isotope polonium-210 in a London hotel.
Former KGB agent and prime suspect Andrei Lugovoi claimed that Berezovsky, whom Russia repeatedly sought to extradite on a wide variety of criminal charges, engineered Litvinenko's death. He said he did to to embarrass the Kremlin and buttress his refugee status.
Berezovsky, who denied the allegations, had spent years supporting the Moscow opposition against Putin, although his name had been discredited among many Russians. Those who received his funding attempted to hide any links to his name.
His case against Abramovich exposed the dirty secrets of Russia's big business in the initial post-Soviet years. He reportedly lost millions of dollars in fees spent on his legal team.
Berezovsky's fortunes dried up on a lavish lifestyle and a posse of bodyguards.
He spent the final months of his life selling his old houses and paintings, including an Andy Warhol print called Red Lenin.