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Alexey Navalny, who has died aged 47, according to the Russian prison service, had long been a thorn in the side of President Vladimir Putin, exposing corruption in high places, campaigning against the ruling United Russia party, and orchestrating some of the biggest anti-government protests seen in recent years.

His imprisonment in 2021 sparked scores of demonstrations across Russia, leading to thousands of detentions. From prison, Navalny denounced Russia’s invasion of Ukraine via social media and encouraged anti-war protests across the country.

The Kremlin critic was quietly relocated to a penal colony in Siberia in December - a move which sparked a two-week search by his team who lost contact with him during the unannounced transfer.

The death of Putin’s most high-profile critic is likely to send shockwaves through parts of Russian society, and punctuates a merciless crackdown on dissidence in Russia that has accelerated during its war with Ukraine.

Navalny was detained and sent to a Russian prison in 2021 after he had returned to Russia from Germany, where he was recovering from Novichok poisoning he blamed on the Russian government. The Kremlin repeatedly denied any involvement.

Dmitry Lovetsky/AP
Alexei Navalny, center, addresses supporters and journalists in Moscow in 2013.

He held no illusions about the risks he faced in his native country, but refused to stay away. Just weeks before leaving Germany, he told CNN: “I understand that Putin hates me, I understand that people in the Kremlin are ready to kill.”

Concerns mounted over Navalny’s health in early April 2023, as his team reported that he was experiencing severe stomach issues and had lost weight.

“We do not rule out that all this time in prison he could have been poisoned with something to make his health deteriorate slowly but steadily,” Navalny’s spokesperson Kira Yarmysh said in a Twitter post on April 11.

Kremlin spokesperson Dmitry Peskov said at the time that the Russian government does not have the “capacity” or “authority” to follow the situation when asked whether Navalny was being poisoned. CNN also reached out to Russia’s federal penitentiary service (FSIN) for comment.

Putin has long refused to utter Navalny’s name. He described the extensive media investigations into the 2020 Novichok poisoning as fabrications by Western intelligence and said in December 2020 that if Russian security services had wanted to kill the activist, they “would have finished” the job.

But Navalny’s death is bound to raise questions in Russia and abroad, in light of his past poisoning and the attacks on other Kremlin opponents before him.

02:36 - Source: CNN
What the life of Putin nemesis in Arctic penal colony looked like

Former Russian agent Alexander Litvinenko died in Britain in 2006 after being poisoned with a rare radioactive isotope, polonium-210.

The nerve agent Novichok nearly killed former Russian spy Sergei Skripal and his daughter in the English city of Salisbury in March 2018. Russia denied responsibility.

In 2015, Russia’s former deputy prime minister Boris Nemtsov, then the most visible leader of the opposition, was gunned down on a Moscow bridge within sight of the Kremlin. Navalny took up Nemtsov’s mantle, becoming Russia’s most prominent opposition figure.

Novichok poisoning

Navalny fell gravely ill in August 2020 while on a return flight to Moscow from the Siberian city of Tomsk. The pilot made an emergency landing in Omsk, where Navalny was taken to hospital for urgent treatment before being transferred to Germany, still critically ill.

The German government said Navalny was poisoned with a chemical agent from the Novichok group, a conclusion supported by two other labs in France and Sweden. Novichok agents are highly unusual, so much so that very few scientists outside of Russia have any real experience in dealing with them.

A subsequent Bellingcat-CNN investigation found that an elite team in Russia’s FSB security service, made up of about six to 10 agents, had trailed Navalny for more than three years. One of those agents revealed in a sting that the lethal nerve agent Novichok had been planted in the activist’s underpants.

Despite these revelations, Navalny said he did not believe there would be an investigation in Russia. “It has become so obvious that it was Putin personally who was behind this,” he said.

Nonetheless, once mostly recovered, the activist announced his plan to go back to Russia, saying: “There was never a question for me whether to return or not, never.”

Alexey Navalny/Instagram/Anadolu/Getty Images
A photo shared on Navalny's instagram account shows the Russian opposition leader in a hospital bed surrounded by his wife and two children as his treatment continues following Novichok poisoning in 2020.

Navalny was detained moments after his return and later jailed on February 2, 2021 after a court ruled he had violated the terms of his suspended sentence in a 2014 embezzlement case he says was politically motivated.

In that case, Navalny was found guilty of fraud after he and his brother Oleg were accused of embezzling 30 million rubles ($540,000) from a Russian subsidiary of French cosmetics company Yves Rocher. Alexey Navalny was given a suspended sentence and his brother was sentenced to a prison term.

Addressing the court in February 2021, Navalny ridiculed claims he broke his parole conditions while recovering from poisoning, pointing out that he was in a coma, then in ICU followed by rehabilitation, and that his lawyer had sent the Russian prison service a notice with details.

He also denounced the Russian President as “Putin the poisoner.”

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While he was in custody ahead of the hearing, Navalny and his Anti-Corruption Foundation (FBK) published an investigation detailing allegations of vast corruption schemes linked to a decadent Black Sea “palace” that Navalny’s team said belonged to Putin. Kremlin spokesman Dmitry Peskov denied the Russian leader was linked to the estate.

In the days ahead of his departure from Germany, Navalny said new criminal cases brought against him in Russia were “demonstratively fabricated” and an attempt to prevent him coming back to his home country.

Russia launched a new fraud accusation and jail threat against Navalny at the end of 2020, increasing pressure on him.

The country’s Investigative Committee has also accused Navalny and his Anti-Corruption Foundation of “fraud on a large scale” for allegedly misusing donations from supporters and spending them on “private purposes.”

Navalny dismissed the charges against him in comments in January 2021. “They are doing everything to scare me. But what they are doing there is not of much interest to me. Russia is my country, Moscow is my city, I miss them,” he said.

He was sent to a penal colony, a two-hour drive from Moscow, to spend the more than two-and-a-half years of his partially suspended prison sentence. In April 2021, Russian press reported that he had been moved to a “medical unit with acute respiratory infections,” and been tested for Covid-19.

The war critic

Even while behind bars, his Instagram and Twitter accounts kept up his attacks on Putin, denouncing Russia’s invasion of Ukraine and advocating anti-war protests across the country.

But it came at a cost, says his allies. Navalny had to fight for even basic rights like boots and medication. His health suffered and he lost weight. His daughter, Dasha Navalnaya, told CNN he was systematically singled out for harsh treatment.

In 2022, Navalny was given a further nine-year sentence on fraud charges he said were politically motivated.

While Judge Margarita Kotova read out the accusations against him, footage showed Navalny as a gaunt figure standing beside his lawyers in a room filled with security officials. He appeared unmoved by the proceedings, looking through some court documents on a table in front of him.

02:41 - Source: CNN
Alexey Navalny's daughter tells CNN her father's health is deteriorating

He was transferred from a penal colony where he was serving his term to a higher security prison facility in Melekhovo, in the Vladimir Region, in June 2022. Months later, he was moved to a solitary prison cell.

His daughter told CNN that prison authorities repeatedly cycled him in and out of solitary confinement. “They put him in for a week, then take him out for one day,” to try to break him, she said. “People are not allowed to communicate with him, and this kind of isolation is really purely psychological torture.”

His physical treatment, she said, was also torturous. “It’s a small cell, six (or) seven-by-eight feet… a cage for someone who is of his six-foot-three height,” she said. “He only has one iron stool, which is sewed to the floor. And out of personal possessions he is allowed to have a mug, a toothbrush, and one book.”

“They’re doing it to shut me up,” Navalny said on X, formerly known as Twitter, in November 2022. “So what’s my first duty? That’s right, to not be afraid and not shut up,” he wrote, urging others to do the same.

“At every opportunity, campaign against the war, Putin and United Russia. Hugs to you all.”

An anti-corruption crusader

Navalny was born in June 1976 in the village of Butyn near Moscow, the son of a military officer.

After graduating in law from Moscow’s Friendship of the Peoples University in 1998, he became a corruption-fighting lawyer who famously branded the United Russia party – founded by Putin – “the party of crooks and thieves.”

He first came to prominence in 2010, when he produced a blog that provided detailed reports on the corruption of Russian state-run companies, including the theft of $4 billion by executives from Transneft, the state-owned pipeline company.

The activist’s investigative videos about the unexplained wealth of top Russian officials provoked the ire of the Kremlin.

Alexander Nemenov/AFP/Getty Images
Navalny appears in a Moscow City Court via a video link from a prison colony during an appeal hearing against his nine-year prison sentence on May 24, 2022.

Navalny’s fierce commitment to his cause led to a rapid rise through the ranks of Russia’s depleted opposition. When anti-government demonstrations broke out in December 2011, he emerged as one of the movement’s leaders. He became a well-known organizer of street protests and vociferously criticized Putin through his blog and on social media.

In 2013, he came second in Moscow’s mayoral election, taking about 27% of the vote. But as with many Kremlin critics, Navalny suffered as his profile rose. He was repeatedly jailed and spent long stretches in custody for organizing political protests.

In July 2019, he was hospitalized with symptoms of an allergic reaction after being held in a special detention center. He expressed suspicion that his condition could have been caused by poisoning, although Russian state news agency TASS reported at the time that doctors found no signs of poisoning.

He was also barred from running for political office over his criminal conviction in the 2014 fraud case – a conviction the European Court of Human Rights ruled was politically motivated.

“The Putin regime is built on corruption,” Navalny told CNN in 2018. “According to official data, over 20% of our population lives below the poverty line. And people link the obvious. Why are we so poor? Because they steal so much,” he said, referring to Russia’s ruling elite.

Asked if he feared for his personal safety, Navalny replied that he had a “clear understanding” of the risks involved in taking on the government.

“But I’m not afraid and I’m not going to give up on what I’m going to do. I won’t give up on my country. I won’t give up on my civil rights. I won’t give up on uniting those around me who believe in the same ideals as me. And there are quite a lot of people like that in Russia,” he said.

Navalny is survived by his wife, Yulia Navalnaya, and their two children.

CNN’s Nathan Hodge, Frederik Pleitgen, Susannah Cullinane, Zahra Ullah, Anna Chernova, Tara John and Lauren Said-Moorhouse contributed to this report.