Mr. Berezovsky may have committed suicide. A lawsuit, in which Mr. Berezovsky had brought a $5.1 billion claim against Roman A. Abramovich in a dispute over the sale of shares in the Russian oil company Sibneft and other assets, ended in a spectacular defeat. Recent news reports described how Mr. Berezovsky had begun to sell personal assets, including a yacht and a painting by Warhol, “Red Lenin,” to pay debts related to the lawsuit. Mr. Berezovsky was a leading Soviet mathematician who after the fall of Communism went into business and figured out how to skim profits off what was then Russian’s largest state-owned carmaker. Along with spectacular wealth, he accumulated enormous political influence, becoming a close ally of Mr. Yeltsin’s. With Mr. Yeltsin political career fading, Mr. Berezovsky helped engineer the rise of Mr. Putin, an obscure former K.G.B. agent and one-time aide to the mayor of St. Petersburg, who became president of Russia in 2000 and last May returned to the presidency for a third term. After his election, Mr. Putin began a campaign of tax claims against a group of rich and powerful Russians, including Mr. Berezovsky and the oil tycoon Mikhail B. Khodorkovsky, who remains jailed in Russia. Mr. Berezovsky fled to London, where he eventually won political asylum and at one point raised tensions by calling for a coup against Mr. Putin.