Former-governor of the sprawling Volga industrial region of Nizhni Novgorod and deputy prime minister under former President Boris Yeltsin, Mr. Nemtsov was once seriously discussed as Mr. Yeltsin's potential successor. Cast into the political wilderness by Putin, Nemtsov has become one of the best known faces of pro-democracy street protest, suffering repeated arrests for participating in "unsanctioned" rallies over the years. Last year he joined with several other leading pro-Western liberals, including former prime minister Mikhail Kasyanov and former independent Duma deputy Vladimir Ryzhkov, to form the Party of Peoples Freedom (PARNAS). Though it appeared to meet requirements for registration under Russia's tough electoral laws, PARNAS was banned and denied the right to field candidates in parliamentary and presidential elections. Nemtsov, who addressed both big Moscow protest rallies, is a dynamic public speaker with strong personal appeal to Russia's youthful and liberal-minded middle class. Russian secret services may consider him dangerous: They paid him what appears to be a back-handed compliment earlier this month by recording his private telephone conversations. Disparaging comments he made about fellow opposition leaders were published in a pro-Kremlin online tabloid.