Feb. 21, 2021: Russian opposition leader Alexei Navalny shows a heart symbol standing in the cage during a hearing to a motion from the Russian prison service to convert the suspended sentence of Navalny from the 2014 criminal conviction into a real prison term in the Moscow City Court in Moscow, Russia.

Feb. 21, 2021: Russian opposition leader Alexei Navalny shows a heart symbol standing in the cage during a hearing to a motion from the Russian prison service to convert the suspended sentence of Navalny from the 2014 criminal conviction into a real prison term in the Moscow City Court in Moscow, Russia. / AP

Prison officials in Russia say opposition leader Alexei Navalny has died in an Arctic penal colony.

They say they're investigating his cause of death. Navalny had been in shaky health after surviving poisoning that he blamed on the Russian government.

The Kremlin denied it. But Secretary of State Antony Blinken says the Russian government - and leader Vladimir Putin - always feared Navalny's opposition to their regime.

We take a look at his life in pictures:

May 8, 2012: Alexei Navalny, a prominent anti-corruption whistle blower and blogger, center, speaks to protesters gathered across the street from the presidential administrations building as a police officer tries to stop him in downtown Moscow.

May 8, 2012: Alexei Navalny, a prominent anti-corruption whistle blower and blogger, center, speaks to protesters gathered across the street from the presidential administrations building as a police officer tries to stop him in downtown Moscow. / AP

May 8, 2012: Alexei Navalny is seen behind the bars in the police van after he was detained during protests in Moscow, on a day after Putin's inauguration.

May 8, 2012: Alexei Navalny is seen behind the bars in the police van after he was detained during protests in Moscow, on a day after Putin's inauguration. / AP

May 24, 2012: Prominent anti-corruption blogger Alexei Navalny greets supporters inside a car after being released from a police station in Moscow. The opposition leader Alexei Navalny received a 15-day sentence for disobeying police during a rally.

May 24, 2012: Prominent anti-corruption blogger Alexei Navalny greets supporters inside a car after being released from a police station in Moscow. The opposition leader Alexei Navalny received a 15-day sentence for disobeying police during a rally. / Reuters

Sept. 8, 2013: Russian opposition leader Alexei Navalny, right, with his wife Yulia, daughter Daria, and son Zakhar leave a polling station in Moscow's mayoral election. Moscow is holding its first mayoral election in a decade.

Sept. 8, 2013: Russian opposition leader Alexei Navalny, right, with his wife Yulia, daughter Daria, and son Zakhar leave a polling station in Moscow's mayoral election. Moscow is holding its first mayoral election in a decade. / AP

March 6, 2015: Alexei Navalny, a Russian opposition leader, walks out of a detention center in Moscow. Navalny walked out of a Moscow detention center a week after fellow opposition leader Boris Nemtsov was shot dead in what his allies say was a political killing aimed at intimidating them.

March 6, 2015: Alexei Navalny, a Russian opposition leader, walks out of a detention center in Moscow. Navalny walked out of a Moscow detention center a week after fellow opposition leader Boris Nemtsov was shot dead in what his allies say was a political killing aimed at intimidating them. / Reuters

September 13, 2015: A man takes a selfie with Russian opposition leader Alexei Navalny, center, near the Open Russia movement office during Russian regional elections in the town of Kostroma, some 300 km outside Moscow. Russians voted September 13 in a regional election expected to yield few surprises, with the country's liberal opposition only able to field a handful of candidates.

September 13, 2015: A man takes a selfie with Russian opposition leader Alexei Navalny, center, near the Open Russia movement office during Russian regional elections in the town of Kostroma, some 300 km outside Moscow. Russians voted September 13 in a regional election expected to yield few surprises, with the country's liberal opposition only able to field a handful of candidates. / AFP via Getty Images

March 26, 2017: Police officers detain anti-corruption campaigner and opposition figure Alexei Navalny during an opposition rally in Moscow.

March 26, 2017: Police officers detain anti-corruption campaigner and opposition figure Alexei Navalny during an opposition rally in Moscow. / Getty Images

March 27, 2017: Russian opposition leader Alexei Navalny gestures while speaking, as his lawyer Olga Mikhailova listens, in court in Moscow, Russia. Navalny, who organized a wave of nationwide protests against government corruption that rattled authorities, was fined 20,000 rubles ($340) on Monday by a Moscow court.

March 27, 2017: Russian opposition leader Alexei Navalny gestures while speaking, as his lawyer Olga Mikhailova listens, in court in Moscow, Russia. Navalny, who organized a wave of nationwide protests against government corruption that rattled authorities, was fined 20,000 rubles ($340) on Monday by a Moscow court. / AP

March 30, 2017: Kremlin critic Alexei Navalny, who was arrested during March 26 anti-corruption rally, gestures during an appeal hearing at a court in Moscow on March 30, 2017.

March 30, 2017: Kremlin critic Alexei Navalny, who was arrested during March 26 anti-corruption rally, gestures during an appeal hearing at a court in Moscow on March 30, 2017. / AFP via Getty Images

Jan. 28, 2018: Russian opposition leader Alexei Navalny, center, attends a rally in Moscow, Russia.

Jan. 28, 2018: Russian opposition leader Alexei Navalny, center, attends a rally in Moscow, Russia. / AP

February 29, 2020: Russian opposition leader Alexei Navalny, his wife Yulia, opposition politician Lyubov Sobol and other demonstrators march in memory of murdered Kremlin critic Boris Nemtsov in downtown Moscow on

February 29, 2020: Russian opposition leader Alexei Navalny, his wife Yulia, opposition politician Lyubov Sobol and other demonstrators march in memory of murdered Kremlin critic Boris Nemtsov in downtown Moscow on / AFP via Getty Images

August 22, 2020: German army emergency personnel load portable isolation unit into their ambulance that was used to transport Russian opposition figure Alexei Navalny at Charite hospital on in Berlin, Germany. Navalny has arrived in Germany at Charite Hospital in Berlin for treatment for possible poisoning.

August 22, 2020: German army emergency personnel load portable isolation unit into their ambulance that was used to transport Russian opposition figure Alexei Navalny at Charite hospital on in Berlin, Germany. Navalny has arrived in Germany at Charite Hospital in Berlin for treatment for possible poisoning. / Getty Images

January 17, 2021: Russian opposition leader Alexei Navalny and his wife Yulia ride on a bus to a terminal of Moscow's Sheremetyevo airport. Navalny returns to Russia from Germany, facing imminent arrest. The 44-year-old is flew back to Moscow after spending months in Germany recovering from a poisoning that he said was carried out on the orders of Pres. Vladimir Putin.

January 17, 2021: Russian opposition leader Alexei Navalny and his wife Yulia ride on a bus to a terminal of Moscow's Sheremetyevo airport. Navalny returns to Russia from Germany, facing imminent arrest. The 44-year-old is flew back to Moscow after spending months in Germany recovering from a poisoning that he said was carried out on the orders of Pres. Vladimir Putin. / AFP via Getty Images

April 28, 2021: Municipal workers paint over graffiti of Russia's imprisoned opposition leader Alexei Navalny in St. Petersburg, Russia . The worlds on the wall reading

April 28, 2021: Municipal workers paint over graffiti of Russia's imprisoned opposition leader Alexei Navalny in St. Petersburg, Russia . The worlds on the wall reading "Hero of our time". / AP

March 22, 2022: Russian opposition leader Alexei Navalny, centre, gestures via a video link provided by the Russian Federal Penitentiary Service, standing next to his lawyer and speaking with Penitentiary Service officers during a court session, in Pokrov.

March 22, 2022: Russian opposition leader Alexei Navalny, centre, gestures via a video link provided by the Russian Federal Penitentiary Service, standing next to his lawyer and speaking with Penitentiary Service officers during a court session, in Pokrov. / AP

Jan. 11, 2024: Russian opposition leader Alexei Navalny appears via a video link from the Arctic penal colony where he is serving a 19-year sentence, provided by the Russian Federal Penitentiary Service during a hearing of Russia's Supreme Court, in Moscow, Russia.

Jan. 11, 2024: Russian opposition leader Alexei Navalny appears via a video link from the Arctic penal colony where he is serving a 19-year sentence, provided by the Russian Federal Penitentiary Service during a hearing of Russia's Supreme Court, in Moscow, Russia. / AP

Tags: Vladimir Putin  corruption  Alexei Navalny  kremlin  russian government