Russian leaders on Friday announced the death of Alexei Navalny, a prominent opposition politician to President Vladimir Putin, in a Siberian prison.

Navalny, 47, had been serving a 19-year sentence for alleged extremism and years of criticism of the authoritarian Putin in a harsh penal colony north of the Arctic Circle. Navalny’s political opposition to Putin and to corruption in Russia had garnered attention around the world for years, especially after Navalny chose to return to Russia after the Kremlin allegedly tried to poison him in 2020.

Navalny, a complex figure, ran for the presidency in Russia in 2018, despite a court ruling him ineligible. After Russia detained him in 2021, he continued to speak out from prison, including against Putin’s now two-year-old war of aggression in Ukraine. Putin, who has essentially ruled Russia as president for more than two decades, is currently seeking a fifth term in office.

Despite not making faith a central component of his political activism, Nalavny has described himself as a Christian and has said that the fact that the Bible provides him guidance has led to “fewer dilemmas” in his life.

Western leaders and others initially responded cautiously or skeptically to the news of Navalny’s death, which came via the official Russian Tass news agency. Navalny’s wife, Yulia Navalnaya, said in a news conference that Putin’s government is “lying constantly.”

In a press conference Friday, President Joe Biden said he was “surprised and outraged” at the reports of Navalny’s death, adding that he has “no reason to believe” the reports of his death are false.

He praised Navalny’s commitment to “calling out Putin’s lies,” noting that he could have “lived safely in exile” after his poisoning but returned to Russia.

Biden called Navalny’s death “yet more proof of Putin’s brutality” and called on Congress to pass aid funding for Ukraine.

“He was so many things that Putin was not. He was brave; he was principled,” Biden said. “God bless Alexei Navalny. His courage will not be forgotten.”

In Navalny’s closing statement during his 2021 trial — which was replete with pop-culture references, as was his style — the opposition leader also spoke about his faith.

“If you want, I’ll talk to you about God and salvation. I’ll turn up the volume of heartbreak to the maximum, so to speak. The fact is that I am a Christian, which usually rather sets me up as an example for constant ridicule in the Anti-Corruption Foundation, because mostly our people are atheists and I was once quite a militant atheist myself,” Navalny said, as reported by the Moscow Helsinki Group, a now-defunct Russian human-rights organization.

“But now I am a believer, and that helps me a lot in my activities, because everything becomes much, much easier. I think about things less. There are fewer dilemmas in my life, because there is a book in which, in general, it is more or less clearly written what action to take in every situation. It’s not always easy to follow this book, of course, but I am actually trying. And so, as I said, it’s easier for me, probably, than for many others, to engage in politics.”

Navalny went on to quote the Bible, specifically the beatitudes passage from Christ’s Sermon on the Mount: “Blessed are those who hunger and thirst for righteousness, for they will be satisfied.”

“I’ve always thought that this particular commandment is more or less an instruction to activity,” Navalny continued.

“And so, while certainly not really enjoying the place where I am, I have no regrets about coming back, or about what I’m doing. It’s fine, because I did the right thing. On the contrary, I feel a real kind of satisfaction. Because at some difficult moment, I did as required by the instructions and did not betray the commandment.”

He added that he believes Russian authorities try to intimidate and isolate people who hold such beliefs. (According to one analysis, religion in Russia is in some ways associated with freedom, perhaps stemming from the historical religious persecution of the atheistic communist regime.)

“We are a very unhappy country. We’re in a vicious circle of unhappiness that we can’t escape from. But, of course, it would be good to, and I am therefore proposing to change our slogan. It’s not enough for Russia to be free; Russia should also be happy. Russia will be happy,” he concluded.

Though he has not commented specifically on reports of Navalny’s death, Pope Francis has repeatedly condemned the violence of Putin’s war in Ukraine and appealed for peace.