(NewsNation) — President Joe Biden warned Russian President Vladimir Putin two years ago about potential consequences should jailed Russian opposition leader Alexei Navalny die in prison, CNN reports.

Though Biden didn’t specify which actions he’d take, during a 2021 summit in Geneva with Putin, he said, “I made it clear to him that I believe the consequences of that would be devastating for Russia.”

Biden added: “What do you think happens when he’s saying it’s not about hurting Navalny, all the stuff he says to rationalize the treatment of Navalny, and then he dies in prison? … It’s about trust. It’s about their ability to influence other nations in a positive way.”

Navalny gained attention by focusing on corruption in Russia’s murky mix of politicians and businesses; one of his early moves was to buy a stake in Russian oil and gas companies to become an activist shareholder and push for transparency.

Who is Alexei Navalny?

Alexei Navalny, the fiercest foe of Putin, died in prison Friday at the age of 47, Russian authorities said.

Navalny, who was serving a 19-year sentence on charges of extremism, felt unwell after a walk, according to the Federal Penitentiary Service, and lost consciousness. An ambulance arrived to try to revive him, but he died. Officials said the cause of death was “being established.”

Kremlin spokesman Dmitry Peskov said Putin was informed of Navalny’s death and the prison service would investigate it in line with standard procedures.

Navalny’s spokeswoman 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 town where he was held.

Shortly after Navalny’s death was reported, the Russian SOTA social media channel shared images of the opposition politician reportedly in court yesterday. In the footage, Navalny is seen standing up and laughing and joking with the judge via video link.

Navalny was born in Butyn, about 25 miles outside Moscow, on June 4, 1976. He received a law degree from People’s Friendship University in 1998 and did a fellowship at Yale in 2010.

Navalny’s poisoning and imprisonment

Before his death, Navalny had been behind bars since January 2021, when he returned to Moscow after recuperating in Germany from nerve agent poisoning that he blamed on the Kremlin.

While serving a jail sentence in 2019 for involvement in an election protest, Navalny was taken to the hospital with an illness that authorities said was an allergic reaction, but some doctors said it appeared to be poisoning.

A year later, on Aug. 20, 2020, he became severely ill on a flight to Moscow from the Siberian city of Tomsk, where he was organizing opposition candidates. He collapsed in the aisle while returning from the bathroom, and the plane made an emergency landing in the city of Omsk, where he spent two days in a hospital while supporters begged doctors to allow him to be taken to Germany for treatment.

Once in Germany, doctors determined he had been poisoned with a strain of Novichok – similar to the nerve agent that nearly killed former Russian spy Sergei Skripal and his daughter in England in 2018 and resulted in the death of another woman.

Navalny was in a medically induced coma for about two weeks, then labored to recover speech and movement for several more weeks. His first communication while recovering showed his defiant wit — an Instagram post saying that breathing on one’s own is “a remarkable process that is underestimated by many. Strongly recommended.”

Additionally, the U.S. State Department said it believed Navalny was poisoned by the Russian security services after he fell ill, according to CNN.

The Kremlin vehemently rejected it was behind the poisoning.

Before his arrest, Navalny 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.

Navalny’s prison conditions

In spring 2020, Navalny went on a hunger strike to protest against prison officials’ refusal to grant proper medical care, according to CNN. During his time in prison, his supporters said Navalny’s health “deteriorated” and his legal team reported his condition was worsened by alleged “torture by sleep deprivation,” per CNN.

Navalny was moved in December from a prison in central Russia to a “special regime” penal colony — the highest security level of prisons in the country — above the Arctic Circle.

His allies decried the transfer to a colony in the town of Kharp, in a region about 1,200 miles northeast of Moscow, as yet another attempt to force Navalny into silence.

In Putin’s Russia, political opponents often faded amid factional disputes or went into exile after imprisonment, suspected poisonings or other heavy repression. But Navalny grew consistently stronger and reached the apex of the opposition through grit, bravado and an acute understanding of how social media could circumvent the Kremlin’s suffocation of independent news outlets.

He faced each setback — whether it was a physical assault or imprisonment — with an intense devotion, confronting dangers with a sardonic wit. That drove him to the bold and fateful move of returning from Germany to Russia and certain arrest.

The Associated Press contributed to this report.