MOSCOW If any single figure embodies the rebellious generation of young Russians who have taken to the streets to try to force out President Vladimir Putin, it is surely Alexei Navalny.
The 37-year-old anti-corruption campaigner, who received a five-year jail sentence for theft on Thursday, was one of the first protest leaders arrested when demonstrations against Putin took off in December 2011.
After 15 days in jail for obstructing police at a Moscow rally, Navalny emerged a hero for the protesters, who chanted his name louder than any other at demonstrations and gave his booming, rabble-rousing speeches the biggest cheers.
By the time the protests started to fade in the spring of 2012, Putin was back in the Kremlin as president while Navalny had established himself as the unofficial but largely undisputed leader of the opposition.
Tall, clean-cut, confident and articulate, Navalny has more potential than any other opposition leader to at least rattle, if not directly challenge, Putin.
Thursday's verdict was seen by many as a sign that the president himself sees him as a threat, even though opinion polls suggest his appeal does not go far beyond the big cities.
"Navalny's sentence looks less like punishment than an attempt to isolate him from society and the electoral process," declared former Finance Minister Alexei Kudrin, a longtime Putin ally respected by many Western economists and politicians.
Navalny has not hidden his presidential ambitions and had been planning to run in September for mayor of Moscow, a potential stepping stone to bigger things, even though opinion polls suggested he had little chance of winning.
His five-year sentence - on charges he denied of stealing from a state timber firm in 2009 - scotches that plan anyway, as well as any ambition to run in the 2018 presidential poll.
But Navalny is an extremely young politician for the former Soviet world, and he can bide his time, even if Putin is re-elected in 2018 for another six years. By 2024, Putin would be over 70 and Navalny would still be under 50.
CATCHING A MOOD
The son of an army officer, Navalny grew up mainly in Obninsk, about 100 km southwest of Moscow. He has a law degree and also studied securities and exchanges.
Navalny represents a new, Internet-savvy generation and is seen as a potential threat to Putin even though the former KGB spy runs a tightly controlled political system that he has crafted in 14 years as prime minister or president.
Navalny operates from a sparsely furnished office just off Moscow's Garden Ring road, one of the capital's main thoroughfares, with a small team assisting him in his campaigning against corruption, mostly centered around his blog.
Usually dressed casually in a T-shirt and jeans, or sometimes in an open shirt without a tie, he looks and sounds different from most Russian political figures - many of whom dress formally in suits and ties.
"Navalny is the only possible leader I see," a Moscow-based Western banker said of Navalny's position in Russia's fragmented opposition, which spent much of the time squabbling during the anti-Putin protests. "He has fire in those blue eyes of his."
Navalny frequently looked disinterested at opposition meetings discussing the protests but came to life at the protests, delivering tub-thumping speeches.
He has managed to grasp a mood change in Russia among the urban youth and growing middle class, still seeking a civil society more than two decades after the Soviet Union collapsed.
"We are not cattle or slaves. We have a voice and we have the strength to defend it," Navalny said in a statement issued during his 15-day jail term for obstructing police in late 2011.
Such simple, defiant phrases quickly caught on, none more that his description of Putin's ruling United Russia as a party of "swindlers and thieves", a tag it has struggled to shake off.
He has also won over supporters with his Internet war on corruption and a lack of fear when taking on the authorities.
"I realize there is danger, but why should I be afraid?" he told Reuters in an interview at the start of the protests.
But indicating he was aware of the risks he faced, he said in a later interview: "You need to understand a very simple thing. To keep himself in power, Vladimir Putin is ready to go very far. Much further than just putting me or anybody else in prison. Much further."
Yet Navalny's character and politics are also more complex than some admiring Western liberals might expect of a Yale-educated lawyer who has taken to buying small stakes in some of Russia's biggest companies to demand greater transparency for shareholders, and the public.
While his time in the United States on a fellowship at Yale has forced him at times into denying accusations from Putin supporters that he is a CIA plant, his hostile views on Muslim and Asian migration into Russia's Slavic heartland have at times obliged him to rebuff suggestions he has "fascist" tendencies.
Once an outspoken Russian nationalist, he was expelled from a liberal opposition party and has promised to crack down on immigration from Central Asia and the Caucasus.
In 2007, Navalny was reported by a state news agency to have been involved in a brawl at a Moscow club. After being ejected by bouncers, he got into a fight on the street and was quoted as saying at the time that he had shot his opponent with an air pistol. Charges were later dropped.
He has toned down his rhetoric over the years and honed his image, focusing on his criticism of the authorities.
Shooting to prominence by challenging state companies such as pipeline operator Transneft to explain millions of dollars of unorthodox payments, Navalny struck a chord with millions of Russians disgusted by the ostentatious wealth of Moscow's elite.
He accused Putin of ruling a venal elite as "chairman of the board of Russia Inc" and, in his latest slight, compared the president to a toad unwilling to get off a pipeline representing Russia's vast oil wealth.
Opinion polls show Putin remains the most popular politician in Russia. But the longer Russia holds off on reforms to boost its economy, the greater Navalny's chances are of building support among frustrated voters in the big cities.
(Additional reporting by Guy Faulconbridge; editing by Tom Pfeiffer)