Alexei Navalny, 44, is Russia’s best-known opposition leader. He has become the international figurehead of dissent against Russian President Vladimir Putin.

For several months, he has been imprisoned in a penal colony in Pokrov, about 60 miles east of Moscow, where his health has deteriorated. He ended a 24-day hunger strike to protest his conditions on April 23, after his doctors expressed alarm that he was close to death. Days later, on April 26, a Russian court in a closed-door hearing ordered Navalny’s headquarters, a network of nearly 40 regional offices, and a number of related social media accounts to suspend activities while it considered a petition to ban them.

Navalny was jailed in January when he flew back to Russia after recovering in Germany from a poison attack in August. He has blamed Russian security forces for the poisoning, as have U.S. and European authorities. Russian officials have denied any role. He was sentenced to more than 2½ years in prison in part for breaching probation rules by going to Germany for the treatment, a ruling his supporters say is entirely political.

U.S. national security adviser Jake Sullivan has warned that Russia will face consequences if Navalny dies while imprisoned.

Despite the risks of demonstrating against Putin, Navalny’s detention has drawn thousands of protesters into the streets in Russia.

Here is what you need to know about Navalny and his imprisonment.

Who is Navalny?

Navalny was born June 4, 1976, in Obninsk, about 60 miles southwest of Moscow.

After earning degrees in law and finance from Russian universities, Navalny entered politics in 1999, just as Putin first took up national leadership. He joined the liberal opposition party Yabloko and pushed it toward a more nationalist message that put him in conflict with party leadership.

He was expelled from Yabloko in 2007, in part because of controversial comments about immigration and his decision to attend the annual Russian March, which is anti-Putin but includes members of the far right.

While running a small corporate law firm in Moscow, Navalny developed a strategy of buying stocks in state-linked oil companies and banks so that he could become a minority shareholder and question the companies’ leadership. He later formed a group known as the Anti-Corruption Foundation to expand this work and open investigations that increasingly struck at the heart of the Kremlin elite. A 2017 exposé alleged that Prime Minister Dmitry Medvedev had a vast, $1 billion network of palaces. The YouTube video accompanying the investigation has received more than 35 million views.

He has played a key role in several political movements.

Has he run for office?

Navalny was barred from running for president in the 2018 election, with the Central Election Commission arguing that his campaign was ineligible because of a conviction in a 2014 embezzlement case that his supporters viewed as political retribution.

When he has been allowed to run, there have been indications of political support. In 2013, he won 27 percent of the vote against a key Kremlin ally in the Moscow mayoral election, a result that surprised some analysts, as Navalny did not have the backing of state media and was forced to travel away from Moscow during the campaign because of legal problems.

Election monitors consistently report violations during Russian elections that compromise their integrity.

What led to his imprisonment and what has happened since?

In August, Navalny was poisoned with a nerve agent while on a flight from Siberia. The pilot made an emergency landing in the city of Omsk, where Navalny was taken to a hospital and placed on a ventilator.

“This is Putin,” Yarmysh wrote on Twitter. “Whether he personally gave the order or not, the blame is entirely with him.”

Navalny was treated in Germany and arrested immediately upon his return to Russia on the basis that he had violated the terms of an earlier parole.

By this spring, his health had deteriorated significantly. His lawyers have said he is experiencing excruciating pain from herniated discs in his back. In late March, Navalny started a hunger strike to demand medical treatment. In mid-April, his spokeswoman said he could have only days to live if he did not receive treatment. Soon afterward, he was moved to a prison hospital.

Navalny announced the end of his hunger strike on April 23 via Instagram. (He does not have access to the account, but his lawyers have said it is run by his allies.)

“Thanks to the tremendous support of good people all over the country and all over the world, we have made tremendous progress,” said the Instagram post. It said he had achieved his goal: access to civilian doctors.

Has he been targeted politically?

In addition to the poisoning in August, Navalny and his supporters point to numerous instances of harassment for his activism, including legal and physical threats.

In 2014, Navalny was sentenced to five years in prison for allegedly embezzling $500,000 worth of lumber from a state-owned company. The prison sentence was later suspended. Though the case was declared unfair by the European Court of Human Rights (ECHR) in 2016, a Russian court reaffirmed it the next year.

Further legal cases have kept Navalny in court or under house arrest. In late 2014, both he and his brother Oleg Navalny were sentenced to prison time for allegedly embezzling money from French cosmetics firm Yves Rocher.

Although Navalny’s sentence was suspended, and the ECHR again said the case was unfair, his brother spent 3½ years in prison before being released in 2018.

Last year, Russian authorities seized Navalny’s bank accounts and those of his wife, son and daughter. After a lawsuit from Yevgeniy Prigozhin, an oligarch close to Putin and the target of an investigation, Navalny was forced to close his Anti-Corruption Foundation in July, but he pledged to continue its work under a different name.

Navalny has also faced physical harassment and threats. In 2017, he was doused with an antiseptic green dye several times. Although he made light of the incident, posing for photographs on his social media accounts, after one incident in April of that year he was hospitalized after the dye went into his eye.

In 2019, Navalny was hospitalized with an “acute allergic reaction” after again being detained. His personal physician said he may have been affected by an unknown chemical substance.

Now Navalny’s main political network in the country is hanging in the balance after a closed Russian court on April 26 ordered it to suspend activities while the court considered a complete ban. The closure would leave Navalny without his organization ahead of Russia’s parliamentary elections in September.

Have other opposition figures been targeted?

Throughout Putin’s long rule of Russia, political opponents have been jailed. For example, Mikhail Khodorkovsky, a Russian oligarch who was initially supportive of Putin, spent 10 years in prison after running afoul of the Kremlin.

Some have been killed. Boris Nemtsov, a liberal politician once considered a potential successor to Putin’s predecessor, Boris Yeltsin, was gunned down just steps away from the Kremlin in 2015. Putin suggested it was a contract killing designed to embarrass the Kremlin.

There have been several high-profile cases of poisonings or alleged poisonings. In 2006, Alexander Litvinenko, a former officer of the Russian Federal Security Service (FSB), died after being poisoned in London.

Litvinenko had written a book that alleged a deadly false-flag conspiracy to help Putin get elected in 1999. British authorities later said that he had been poisoned after drinking tea laced with polonium-210 and that Putin himself may have ordered the killing.

This report has been updated.