A charismatic anti-corruption campaigner, Alexei Navalny has been Russia's leading opposition politician for around a decade, determined to challenge Vladimir Putin's grip on power despite frequent prison stays and even harm to his health.
The Yale-educated 44-year-old lawyer -- who was discharged from a hospital in Germany after treatment for a poisoning attack in Siberia -- has been banned from state television and was barred from challenging Putin in the 2018 presidential election.
Despite being frequently jailed and physically attacked, he has vowed to continue in politics and says he will return to Russia after fully recovering from being poisoned with the Novichok nerve agent in Siberia in August.
He has appeared gaunt in social media posts since the poisoning his allies say was sanctioned and carried out by the state and led to his month-long hospitalisation.
But the staunch Kremlin critic has also taken an upbeat tone in the posts, thanking his wife for her support and mocking the Kremlin for suggesting he poisoned himself.
Navalny has won a young fan base through viral videos exposing corruption among the elites and has more than two million followers on Twitter.
He has grabbed attention with his uncompromising rhetoric and coined phrases such as the "party of crooks and thieves" to slam the ruling United Russia party.
In 2011, the anti-corruption blogger led mass protests when tens of thousands took to the streets of Moscow to protest vote-rigging in parliamentary elections.
Two years later the father of two stood for Moscow mayor, coming second against Putin ally Sergei Sobyanin.
- Brother jailed -
In 2017, he accused then-prime minister Dmitry Medvedev of massive corruption in a YouTube documentary. That kick-started a fresh wave of protests across the country that was met with police violence and mass arrests.
The same year he had to travel to Spain for surgery after one of several street attacks left him nearly blind in one eye.
Navalny has faced a series of legal cases, which supporters see as punishment for his activism.
In 2013, he was found guilty in an embezzlement case involving a timber deal and given a five-year suspended sentence that disqualified him from running in elections.
In 2014, he was given another suspended sentence, and his brother Oleg, a co-defendant, was jailed for three-and-a-half years in a decision activists likened to a "hostage-taking".
Navalny has said he learnt about political campaigning from watching the US television series "House of Cards" and once listed Hollywood actor-turned-politician Arnold Schwarzenegger among his personal heroes.
But with the Kremlin tightly controlling the media, he still remains a fringe figure for many Russians, who are exposed to the official portrayal of him as a Western stooge and convicted criminal.
Putin has refused to pronounce Navalny's name in public, instead referring to him as "the person you mentioned", among other euphemisms, when asked directly about the opposition leader.
- Eye-catching exposes -
While barred from mainstream politics, Navalny has sought to expose the lavish wealth of Russia's elites, broadcasting the findings of his investigations to millions of Russians on social media and YouTube.
Among Navalny's most eye-catching exposes have been details on the palatial homes of Putin's allies in Russia and abroad -- including one kitted out with a vast climate-controlled storage room for fur coats.
But despite tapping into discontent among a largely young urban middle class he is far from a unifying opposition figure, and some have criticised his anti-immigrant nationalist stance.
He scored his biggest recent success in local elections last year, when pro-Putin parties suffered unprecedented losses because of a "Smart Voting" plan Navalny put forward after his allies were barred from standing in numerous races.
The tactic calls for voters to support the one opposition candidate most likely to defeat the ruling party and saw Kremlin-linked candidates drop seats in the Moscow assembly.
His allies claimed symbolic victories in local elections in Siberia this month, citing the strategic voting tactic.
Since last year's elections, however, Navalny's offices have been raided repeatedly, while his Anti-Corruption Foundation was declared a "foreign agent" and ordered to pay several large fines.