Russian opposition figures: Boris Nemtsov
The BBC looks at some of Russia's key opposition figures.
Boris Nemtsov, 52, is one of Russia's veteran liberal politicians. He was born in Sochi on the Black Sea, to Jewish parents, and studied radiophysics in the industrial city of Nizhny Novgorod (formerly Gorky).
In the 1990s, after the collapse of the Soviet Union, he used his position as governor of Nizhny Novgorod to open up the region to the free market - and drew the interest of President Boris Yeltsin.
He served as deputy prime minister under Yeltsin, with special responsibility for energy, and in 1999 co-founded the liberal-democratic Union of Right Forces.
In an interview in 2010 he warned that "there should not be any illusions about the country waking up rapidly because Putin has plunged it into a deep, almost hopeless hibernation".
In 2004 he supported Ukraine's Orange Revolution and became an economic adviser for Viktor Yushchenko, who ousted the presidential candidate backed by Mr Putin - Viktor Yanukovych.
Mr Nemtsov co-founded the anti-Putin movement Solidarity in 2008 with chess champion Garry Kasparov - an effort to unite various opposition groups.
In January 2011 Mr Nemtsov was sentenced to 15 days in jail after taking part in a New Year's Eve opposition rally.
His fluent English has made him a well-known spokesman for the Russian opposition on international media.
In December 2011 he apologised to some fellow opposition activists for insults leaked from his private phone calls. He said the publication was part-truth, part-fabrication and accused the Kremlin of a "provocation".
He is married and has four children.