Alexei Navalny has become the latest in a string of deaths of critics of Russian President Vladimir Putin.
Over his more than two decades at the top of the Kremlin, a number of Mr Putin’s opponents have suffered unfortunate fates – including being jailed, shot dead in the street, or poisoned with tea spiked with polonium-210.
Who are the people who have dared speak out against Mr Putin or defy the Kremlin, and where are they now?
Alexei Navalny
Born to factory owners in a village west of Moscow, Alexei Navalny grew to become perhaps the highest-profile critic of Mr Putin’s time in power.
His political activism, including extensive investigations into high-level corruption and running to be mayor of Moscow, gained him fame – and many believed he posed a threat to Mr Putin.
It was in August 2020 when his fight against the Russian president hit the global headlines.
Mr Navalny fell gravely ill on a flight from Siberia to Moscow and he was flown, still in a coma, to Berlin.
His team accused the Kremlin of poisoning him, a charge the Kremlin denied.
German medics confirmed that he had been poisoned with novichok – a Soviet-era nerve agent – and his recovery took months.
Despite the danger, Mr Navalny elected to return to Russia where he was later arrested, convicted on charges he says are politically motivated, and sent to a Russian penal colony.
In February this year, Russian officials said Mr Navalny died in prison.
Boris Nadezhdin
Opposition politician Boris Nadezhdin declared that he would run against Mr Putin in the 2024 presidential election.
Despite doubts that the 60-year-old could present a serious challenge to the incumbent leader, Mr Nadezhdin said he had gathered more than 200,000 signatures from across Russia.
He had surprised some analysts with his strong criticism of what the Kremlin calls its “special military operation” in Ukraine, calling the war a “fatal mistake” and vowing to try to end it through negotiations.
On 8 February, he said he had been barred from running in the election and the Central Election Commission said it had found flaws in signatures his campaign had collected.
He vowed to appeal to Russia’s supreme court, adding: “Taking part in the presidential election in 2024 is the most important political decision of my life. I am not giving up on my intentions.”
Speaking to Sky News last year, Mr Nadezhdin said he was not afraid of speaking out “because I have a long life” and he had faced death several times.
Yevgeny Prigozhin
The ascension of Yevgeny Prigozhin from a hot dog seller to the boss of a private army which marched on Moscow was remarkable.
His Wagner Group mercenaries were notorious both for their brutality in Ukraine but also their influence in Africa.
Prigozhin became increasingly bold in his criticism of the Russian military and its top command.
When his forces began a march on Moscow from the southern city of Rostov it appeared to be the biggest challenge to Mr Putin for decades, but the apparent coup attempt fizzled halfway to the capital.
In August 2023, he died a fiery death when the private plane he was on crashed north of Moscow, raising suspicions of Kremlin involvement.
The Kremlin denied assassinating Mr Prigozhin, calling accusations of Mr Putin’s involvement “an absolute lie”.
Anna Politkovskaya
On 7 October 2006 – Mr Putin’s birthday – journalist Anna Politkovskaya was shot in the lobby of her apartment building.
Before her death, she had specialised in investigating human rights abuses in Chechnya and corruption more broadly.
Her killing led to claims that Mr Putin had not done enough to protect the media.
He described the murder as “abominable in its cruelty” and commented that her death caused more problems for the Kremlin than her work.
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Who is jailed opposition leader Alexei Navalny?
Boris Nemtsov
A former deputy prime minister of Russia under President Boris Yeltsin, Boris Nemtsov was a fierce critic of Putin and a prominent opposition leader.
He had been working on a report examining Russia’s role in the conflict in Ukraine in 2015.
But, aged 55, he was killed before it was finished. Mr Nemtsov was shot dead on a bridge just metres from the Kremlin as he walked home at night with his girlfriend.
Five men were found guilty of organising and carrying out the contract killing. Zaur Dadayev, an officer in Chechen leader and Putin ally Ramzan Kadyrov’s security forces, was found guilty of firing the fatal shots.
The Kremlin denied involvement in the killing.
Alexander Litvinenko
A former agent with the Russian FSB security service, Alexander Litvinenko fled Russia and eventually gained British citizenship.
He had accused Mr Putin of corruption and also blamed him for the infamous Moscow apartment bombings which Mr Putin, then prime minister, had used as a reason to start the Second Chechen War in 1999. It proved hugely popular and helped bring him to power.
Litvinenko died in November 2006, weeks after drinking tea that had been poisoned with polonium-210, a rare and very potent radioactive isotope.
The poison was ingested during a meeting with two Russian spies at the Millennium Hotel in London and the killing is thought to have been signed off by Putin himself. Russia has always denied any involvement.
Garry Kasparov
Regarded as one of the greatest chess players of all time, Garry Kasparov has been living in exile in New York since 2013.
The former world champion had become an impassioned campaigner against Mr Putin’s rule and took part in some of the mass opposition street protests organised by Alexei Navalny.
He has said he fears arrest were he to return to Russia.
Ravil Maganov
The chairman of the board of Russia’s second largest oil producer Lukoil, Ravil Maganov had openly criticised the war in Ukraine.
In a statement in March 2022, the board called for the “soonest termination of the armed conflict” and expressed “sincere empathy for all victims”.
It added: “We strongly support a lasting ceasefire and a settlement of problems through serious negotiations and diplomacy.”
In September that year, 67-year-old Mr Maganov died after apparently falling from a sixth-floor window at the Central Clinical Hospital in Moscow.
Paul Klebnikov
Investigative journalist, Paul Klebnikov, an American of Russian descent, was killed outside his office in a drive-by shooting in Moscow in 2004.
He was the editor of Forbes Russia and had written about corruption.
Forbes had also published a list of the country’s richest people.
Natalia Estemirova
Natalia Estemirova was an award-winning human rights campaigner who had collected evidence of abuses in Chechnya since the start of the second war there in 1999.
She was kidnapped near her home on 15 July 2009 in the Chechen capital, Grozny.
Several hours later her body was found in an area of woodland, with gunshots wounds to the head and chest.
Then president Dmitry Medvedev rejected claims that Chechnyan leader Ramzan Kadyrov was responsible and suggested the killing had been carried out to discredit the Kremlin.
Denis Voronenkov
A former Russian politician, Denis Voronenkov was an outspoken critic of Mr Putin.
Previously a member of the communist faction in the lower house of Russian parliament, Mr Voronenkov fled to Ukraine in 2016 and was granted Ukrainian citizenship.
He was shot and killed in Kyiv in March 2017.
Ukraine’s then president Petro Poroshenko described his killing as an “act of state terrorism” by Russia – an accusation rejected by the Kremlin.
Boris Berezovsky
Former billionaire Boris Berezovsky had been living in exile in Britain since 2000 when he was found dead in 2013.
He made his fortune in Russia in the 1990s during the mass sell off of state assets following the collapse of the Soviet Union.
Once incredibly rich, in his later years his fortune is believed to have dwindled.
James Nixey, head of Chatham House’s Russia programme, previously described him as “the most virulently anti-Kremlin, anti-Putin of the oligarchs”.
“He was certainly willing to spend his money, what little he had left, in an attempt to use it to end the current regime in Russia.”
Mr Berezovsky was found dead at his home in Berkshire. An inquest recorded an open verdict amid conflicting evidence about the way his body was found hanged.
Sergei Skripal
Formerly a colonel with Russian military intelligence before leaving in 1999, Sergei Skripal went on to work at the country’s foreign ministry until 2003.
He was arrested in Moscow a year later and confessed to having been recruited by British intelligence in 1995.
He said he had given information to British intelligence about Russian agents in Europe in return for around $100,000 (£79,300).
Mr Skripal was jailed but later released in a spy swap and moved to the UK.
In 2018, along with his daughter, he was poisoned with the nerve agent novichok but the pair survived the attack.
The Kremlin denied that Russia was in any way involved in the poisoning, describing British accusations that an attack had been approved by senior Russian officials as “unacceptable”.
Sergei Yushenkov
Liberal Russian politician Sergei Yushenkov was shot dead in a Moscow suburb in 2003.
A member of the State Duma and former colonel in the Soviet army, Mr Yushenkov was shot several times outside his apartment building.
He had been involved in setting up the Liberal Russia Party, which had achieved full registration just hours before he was killed.
Mr Yushenkov had been willing to speak out against Putin and the war in Chechnya.