Berezovsky later sued a Russian broadcaster for libel after it claimed in a report that he was behind the death of Litvinenko.
He won the claim against All-Russian State Television and Radio Broadcasting Company, and the High Court in London awarded him 150,000 pounds ($223,400) in damages.
From math professor to oligarch
Berezovsky began his working life as a math professor and then became a 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.
Businessmen 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 Putin for president, pouring money into the latter's political party.
Fall from political favor
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.
"He was obviously very ambitious, and he wanted, I think, to be in political control of Russia during Yeltsin's time, and that didn't work out for him," said Stuart Loory, a former Turner Broadcasting System executive vice president, who was a consultant to Berezovsky during the 1990s.
Berezovsky did not have an easy time of it as an oligarch.
"There were two attempts on his life, 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," Loory said.