Alexei Navalny, Russian President Vladimir Putin’s fiercest enemy, who crusaded against official corruption and organized mass anti-Kremlin protests, died in prison on Friday, Russia’s prison agency said. He was 47 years old.

The Federal Penitentiary Service said in a statement that Navalny felt unwell after a walk on Friday and lost consciousness. An ambulance arrived to try to rehabilitate him, but he died.

Kremlin spokesman Dmitry Peskov says Putin was informed of Navalny’s death and that the prison service was investigating the death according to standard procedures.

Navalny’s spokesperson, Kira Yarmysh, said on X, the platform formerly known as Twitter, that the politician’s team had no confirmation of his death so far and that his lawyer was traveling to the city where he was detained.

Navalny, who was serving a 19-year sentence on extremism charges, was transferred in December from his former prison in the Vladimir region of central Russia to a “special regime” prison colony (the highest prison level security in Russia) above the Arctic Circle.

His allies denounced the move to a colony in the town of Kharp in the Yamalo-Nenets region, about 1,900 kilometers (1,200 miles) northeast of Moscow, as yet another attempt to force Navalny into silence.

The remote region is famous for its long and severe winters. Kharp is about 100 kilometers (60 miles) from Vorkuta, whose coal mines were part of the Soviet gulag prison camp system.

Navalny had been behind bars since January 2021, when he returned to Moscow after recovering in Germany from a nerve agent poisoning that he blamed on the Kremlin. Before his arrest, he campaigned against official corruption, organized major anti-Kremlin protests, and ran for public office.

He had since received three prison sentences, all of which he rejected as politically motivated.

In Putin’s Russia, political opponents often disappeared amid factional disputes or went into exile after imprisonment, suspected poisoning or other harsh repressions. But Navalny consistently grew stronger and rose to the top of the opposition through courage, bravery and a deep understanding of how social media could bypass the Kremlin’s suffocation of independent media.

He faced every setback, whether physical assault or imprisonment, with intense devotion, meeting dangers with sardonic wit. That led to the bold and fateful decision to return from Germany to Russia and certain arrest.

Navalny was born in Butyn, about 40 kilometers (25 miles) from Moscow. She earned a law degree from People’s Friendship University in 1998 and a fellowship at Yale in 2010.

It gained attention by focusing on corruption in Russia’s murky mix of politicians and businesses; One of his first moves was to buy a stake in Russian oil and gas companies to become an activist shareholder and drive transparency. By focusing on corruption, Navalny’s work had pocket appeal to the widespread sense that Russians were being deceived, and had a stronger resonance than more abstract and philosophical concerns about democratic ideals and human rights.

He was convicted in 2013 of embezzlement in what he called a politically motivated prosecution and sentenced to five years in prison, but later, shockingly, prosecutors demanded his release pending appeal. A higher court later imposed a suspended sentence on him.

The day before the sentencing, Navalny had registered as a candidate for mayor of Moscow. The opposition saw his release as a result of large protests in the capital over his sentencing, but many observers attributed it to the authorities’ desire to add a touch of legitimacy to the mayoral election.

Navalny finished second, an impressive performance against the incumbent who had the backing of Putin’s political machine and was popular for improving the capital’s infrastructure and aesthetics.

Navalny’s popularity surged after top charismatic politician Boris Nemtsov was shot dead in 2015 on a bridge near the Kremlin.

Whenever Putin spoke about Navalny, he made sure to never mention the activist by name, referring to him as “that person” or similar words, in an apparent effort to diminish his importance.

By Sam