Alexei Navalny, the prominent Russian opposition leader and fierce critic of President Vladimir Putin, reportedly died in a Russian prison at the age of 47. Russia’s prison agency confirmed his death on Friday.

What Happened: Navalny, who was known for his anti-corruption activism and large-scale anti-Kremlin protests, passed away in prison on Friday, the Associated Press reported. The Federal Prison Service stated that Navalny fell ill after a walk and subsequently lost consciousness. Despite efforts to revive him, he did not survive.