The murder of Boris Nemtsov, Russia's most high-profile and charismatic opposition leader has sent shockwaves across Russia, and drawn condemnation from across the world.
Barack Obama, David Cameron, Angela Merkel and Garry Kasparov were among those who called for a through investigation into the killing of one of Vladimir Putin's key rivals - a death the Russia President has said he will investigate personally.
But who was Boris Nemtsov? These are 19 things you need to know:
The life of Boris Nemtsov
Boris Nemtsov was one of the most outspoken and charismatic critics of President Vladimir Putin.(01 of19)
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He was gunned down within metres of the Kremlin, shot four times in the back in a murder which was called an "assassination" by his supporters.(02 of19)
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Nemstov was born in Sochi to a Jewish mother, but baptised by his Russian Orthodox paternal grandparents.(03 of19)
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He was an talented physicist, and worked at a research fellow at a university in Gorky, 250 miles from Moscow(04 of19)
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He was deeply politicised by the Chernobyl nuclear disaster, and first came to prominence organising a protest movement in his hometown to stop the construction of a nuclear power plant(05 of19)
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In 1990, he won a seat in the Parliament aged 30, and joined the progressive centre-left faction, where he would become close to Boris Yeltsin(06 of19)
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He stood on the tank with Yeltsin at his famous speech to protesters in 1991(07 of19)
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Nemtsov served as a regional governor and then a deputy prime minister in the 1990s and once was seen as a possible successor to Yeltsin, who became Russia's first elected president.(08 of19)
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His economic reforms won him praise from Margaret Thatcher, but the party he founded in the late 90s, Union of Right Forces, was controversial among many Russians for its policy of privatisation, and the several economic crises suffered during the period(09 of19)
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His party eventually lost all seats in the Duma which was dominated by Putin's United Russia party(10 of19)
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During his time in politics, he was widely liked for his good humour, but he and other top opposition figures have disappeared from state television, denied a platform(11 of19)
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Nemtsov became an opposition figurehead, leading protest marches against state corruption and being frequently arrested(12 of19)
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He was regularly threatened on social media by Russian nationalists and received death threats(13 of19)
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In his 2009 campaign to be mayor of Sochi, ammonia was thrown in his face (14 of19)
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Nemtsov was close to firebrand opposition leader and blogger Alexei Navalny, the new, young face of the opposition movement - who is currently serving a short prison sentence(15 of19)
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Nemtsov said earlier this month that his 86-year old mother was afraid that Putin could have him killed. Asked if he had such fears himself, he responded: "If I were afraid I wouldn't have led an opposition party"(16 of19)
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At the time of his death, Nemtsov was working on a report presenting evidence that he believed proved Russia's direct involvement in the separatist rebellion that has raged in eastern Ukraine since April. (17 of19)
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Just hours before his death Nemtsov was on Russian radio urging Muscovites to take part in a peace rally against Russian involvement in the war in Ukraine and the financial crisis in Russia, scheduled for Sunday(18 of19)
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He was killed in front of his girlfriend Anna Durytska, a Ukrainian model, less than 200 metres from the Kremlin, shot four times as he crossed the Bolshoy Moskvoretsky Bridge (19 of19)
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