(CNN) -- The colorful Boris Berezovsky, who died in unexplained circumstances over the weekend at a country estate south of London, was one of the Russian oligarchs who made fortunes following the breakup of the former USSR.
But by the time of his death the 67-year-old was reportedly in financial difficulties after he was ordered to pay a massive divorce settlement to his ex-wife as well as legal costs following the loss of a $6.5 billion lawsuit against fellow oligarch Roman Abramovich last year.
His high-stakes later years were a far cry from his earlier career as a Moscow math professor and systems analyst who switched to more lucrative jobs in post-Soviet Russia, said CNN's Jill Dougherty, who interviewed him many times.
Berezovsky went on to sell cars "at a time when that was a luxury," she said.
"There were a lot of people who wanted to buy them, and he parlayed that -- as so many of these oligarchs did -- into something much, much bigger."
While Berezovsky made a good portion of his money from luxury car sales, his wealth and political influence skyrocketed when he bought into Russian media.
He invested in the Moscow Independent Broadcasting Corp., which -- with TBS as a partner -- founded Moscow's first independent television station, TV-6.
Under President Boris Yeltsin, the Russian Federation's first president from 1991 to 1999, "there were really no rules governing anything," Dougherty said.
Businessmen who came to be known as oligarchs amassed massive wealth and political influence in the 1990s during the privatization of Russia following the fall of the Soviet Union.
Those like Berezovsky wound up lending the fledgling Russian government money "when it was desperate for money," Dougherty said. "These guys picked up companies on the cheap -- for pennies on the dollar."
A year or two later, the companies were worth much more, and the owners became wealthy.
In return for backing Yeltsin, Berezovsky gained political influence within the Kremlin. He later backed Vladimir Putin for president, pouring money into the latter's political party.
But after he was elected, Putin saw that the oligarchs had the potential to gain too much political power and moved to thwart them, Dougherty said.
It has been widely reported that Putin resented the meddling of the oligarchs, particularly Berezovsky.
Berezovsky did not have an easy time of it as an oligarch. "There were two attempts on his life," said Stuart Loory, a former Turner Broadcasting System executive vice president and a former consultant to Berezovsky.
"One at his country home outside Moscow in a gated community. Somebody planted a bomb in his car and, fortunately, it didn't work very well. And the other was when he was leaving his club and there was a car bomb in the car and his driver was killed and he escaped without injury."
Within months of Putin's election in 2000, the government began trying to collect on tax claims against the oligarchs, including Berezovsky, who fled to Britain.
Berezovsky began agitating from Britain against Putin, calling for a coup to oust the Russian president.
In 2003, as Russia was seeking his return, Berezovsky was granted political asylum by British authorities after they realized he was wanted on political grounds, not criminal, according to published reports at the time. The case strained relations between Moscow and London.
Berezovsky was convicted of fraud and tax evasion in absentia by a Russian court in 2007. He also accused Russia of trying to assassinate him, and eventually befriended Alexander Litvinenko, the FSB (the KGB's successor) agent who claimed to have been sent to kill him.
Litvinenko himself died at a London hospital November 23, 2006, from a massive dose of the radioactive material polonium-210. In a deathbed statement he blamed Putin for his death, something the Kremlin strongly denied.
Berezovsky later won libel damages in London over allegations that he was involved in Litvinenko's death, which were broadcast April 1, 2007, on RTR's news program Vesti Nedeli, or News of the Week.
But he is believed to have been in serious financial difficulties after running up huge legal fees in recent years.
In 2011 he paid out what was reported to have been Britain's biggest-ever divorce settlement to ex-wife Galina Besharova. The Daily Telegraph said the settlement was worth up to £220 million ($330 million).
And Berezovsky made headlines the following year after losing what was called one of the most expensive private lawsuits in history against Abramovich, a former friend and ally.
Berezovsky sued Abramovich, owner of Chelsea Football Club, for $5.1 billion, alleging that he was forced to sell his stake in the Russian oil company Sibneft for a fraction of its true value.
The judge called Berezovsky's testimony unreliable and, at points, dishonest.
Analysts put the price tag for legal fees alone at more than $250 million spent between the two sides, which Berezovsky was ordered to pay.
Berezovsky was this year reported to be in serious financial difficulties; last week he sold an Andy Warhol screen print entitled "Red Lenin" for $200,000 and the mansion where he died was reported to be owned by his ex-wife.
As speculation swirled about the cause of his death, Damian Kudriavtsev, a friend of Berezovsky, said Sunday that his friend was unhappy and was in financial trouble, but wouldn't have harmed himself.
Berezovsky, he said, had always hoped to return to Russia someday.
About two months ago, he sent a letter to Putin asking permission to return to Russia, Putin spokesman Dmitry Peskov said. "He admitted that he had made a lot of mistakes, asked forgiveness for the mistakes and asked Putin to let him return home," Peskov said, according to a duty officer with the presidential press service.
It's unknown whether Putin responded to the letter, but Berezovsky did not return.