He's been partially blinded after toxic chemicals were hurled in his face, almost died after being allegedly poisoned by the Kremlin in Siberia, and this March, was sentenced to nearly a decade in a Russian maximum-security prison.
But the spirit of Alexei Navalny — the man described as Russian President Vladimir Putin's "public enemy No 1" — remains intact, allies of the 45-year-old lawyer turned opposition leader have told The Australian.
"He is a very strong person. He doesn't want to show Putin any weakness or indication that he is ready to give up in any way," anti-corruption lawyer Lyubov, who began working with Navalny in 2011, said.
"Even though he knows that Putin will try to keep him in prison for as long as he can and that his sentence can be extended any time.
"Navalny realises that he is being watched by the millions of Russians who support him and he tries to set an example with his strength of spirit, even in the tough conditions of a Russian prison."
The father-of-two — who, born in 1976 to a military family near Moscow, rose from obscurity to become the dictator's biggest domestic opponent — has been exposing Kremlin corruption since 2008.
Putin first tried to put him behind bars 10 years ago, when prosecutors charged Navalny with embezzling timber.
When that didn't stick, they filed new charges months later, accusing him and his brother, Oleg, of stealing from two companies.
While both men were sentenced to three and a half years in prison, only Oleg served time. Navalny's sentence was suspended, one Kremlin-aligned newspaper noting at the time that putting him behind bars "could turn him into Russia's version of Nelson Mandela".
In the following years, as his campaign to dislodge the long-serving president inspired unprecedented street protests that, at their height, involved tens of thousands of people marching through Moscow chanting "Putin is a thief", his family's flat was repeatedly raided by police.
And in 2017, he nearly lost the use of his right eye when a pro-Kremlin activist threw chemicals into his face.
But it wasn't until August 2020, as he returned to Moscow from Siberia where he had lent his support to local activists, that Navalny's life was truly threatened, when he collapsed in agony on the flight home.
After an emergency landing, he was rushed to hospital in a critical condition. While Russian officials put forward overwork, too much alcohol and a "simple lack of breakfast" as explanations for his violent illness, the truth was much more sinister.
Doctors in Berlin, where Navalny was flown for medical treatment, found after a number of tests that the activist had been targeted with a form of Novichok — the Soviet-era nerve agent — smeared onto his underpants by Federal Security Service (FSB) agents, which then passed through his skin into the bloodstream.
The crime — which Navalny uncovered himself, with the help of investigative journalism website Bellingcat — was made a joke of by Putin, who refuses to say his opponent's name aloud.
"Who needs him?" the President said of Navalny with a laugh, when asked during a press conferences about the allegations that he'd ordered the hit.
If Russia had wanted to poison "the Berlin patient", Putin added, "we would probably have finished the job".
Several months after the poisoning, Navalny felt well enough to resume his activism, and last year, made the decision that he "knew" he had to "from the moment I opened my eyes".
Despite warnings from Russian authorities that he would be arrested upon his return because he had failed to check in with his parole officer while he was in Germany, Navalny and his wife Yulia flew back to Moscow on January 17.
At passport control, several officers approached him and led him away, to the capital's Penal Colony No 2 — the infamous prison camp where he was incarcerated until his trial this March.
Along with Navalny and his supporters, Western governments and human rights groups say that all charges against him are politically motivated and aimed at stifling his attempts to challenge Putin at the ballot box.
Asked whether he had been prepared for the leader's furious revenge upon returning to Russia, Sobol told The Australian: "Inasmuch as anyone could be ready for an assassination attempt or to be imprisoned for an undetermined period. He has always been aware that some kind of … self-sacrifice would be necessary."
"The story of Navalny has the makings of an epic. It's almost biblical," Vladimir Ashurkov, a former banker who is now the executive director of Navalny's FBK anti-corruption group, told the broadsheet.
"He's a brave hero poisoned by his opponent, the tsar, and he miraculously survives assassination. He recuperates and talks to one of his assassins. And then, despite all the threats, he returns to his home country where he is imprisoned but still sends his diatribes from behind bars and from his trial.
"This is a heroic story. And, you know, I don't think we are at the end of it yet."
After his sentencing two months ago, Navalny tweeted that he and his supporters would continue to fight the Kremlin's censorship, in order to "bring the truth to the people of Russia".
"I am very grateful to everyone for their support. And, guys, I want to say: the best support for me and other political prisoners is not sympathy and kind words, but actions," he wrote.
"Any activity against the deceitful and thievish Putin's regime. Any opposition to these war criminals.
"In 2013, after hearing my first verdict, I wrote this and now I will repeat it: don't be idle. This toad sitting on an oil pipe will not overthrow itself."