Who is Paul Whelan, the former US Marine who Russia branded a spy?

Former US Marine Paul Whelan has been released from a Russian prison after more than five years in custody.

Mr Whelan, 54, was given a 16-year jail sentence in 2020 after being detained in Moscow two years earlier on suspicion of spying.

The Michigan native had been left out of two previous prisoner swaps, including the one that freed US women's basketball star Brittney Griner.

President Joe Biden, who pledged to "never give up" on securing his freedom, hailed the release of Mr Whelan and 15 other Westerners on Thursday as "a feat of diplomacy".

The US had previously designated Mr Whelan as "wrongfully detained" - a classification that committed the government to work on his release.

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Who is Paul Whelan?

Mr Whelan is a citizen of four countries - the US, Canada, the UK and the Republic of Ireland.

From Novi, Michigan - a suburb of Detroit - he was born in Canada to British parents and moved to the US as a child.

Military records show he joined the US Marine Corps Reserves in 1994, about six years after reportedly working in law enforcement as a police officer and sheriff's deputy in Michigan.

He started as an IT project manager for a company called Kelly Services in the early 2000s, but deployed with the Marines within a couple of years on the first of two tours to Iraq, in 2004 and then 2006.

It was while serving in the Marines that he made his first trip to Russia, a visit he detailed on his website, which was shut down several years ago.

Sharing pictures of the visit, he described having a "quite enjoyable time" exploring the cities of Moscow and St Petersburg.

But in 2008, Mr Whelan - who had by then achieved the rank of staff sergeant - was discharged from the Marines for bad conduct.

The Pentagon, which released his records, said the charges related to larceny. CNN reports he was accused of using someone else's social security number, and "writing bad cheques".

His family was reportedly unaware of these events.

Mr Whelan continued to work for Kelly Services, and was promoted to senior manager of global security and investigations in 2010.

According to court documents, he was in charge of the company's campus security group, and his duties included managing and conducting investigations, as well as handling some purchasing.

He left the company in 2016, moving to become director of global security for US-based automotive components supplier BorgWarner.

Mr Whelan was "responsible for overseeing security" at facilities in Michigan and around the world, a company statement said. The company does not have any facilities in Russia, but the former Marine often travelled there.

Why was Whelan in prison?

Since his first visit in 2006, Mr Whelan made a number of other trips to Russia and developed an in-depth knowledge of the country.

It was due to his knowledge of Russia that he had been asked to attend the wedding of a fellow former Marine in Moscow in December 2018, his brother David told the BBC's Newshour after his arrest.

"His experience of having already been to the Kremlin and walked around Red Square and navigating the metro, his friend felt Paul could assist a bunch of Americans who hadn't otherwise ever been to Moscow," David Whelan said.

On 28 December, however, he was arrested by Russia's FSB state security agency, which claimed he had been "caught spying" in Moscow. At the time, there were uncorroborated reports he had been caught receiving a digital storage device containing a list of intelligence officials.

There was also speculation over other possible motives for the arrest, which included a suggestion Mr Whelan was detained so he could be exchanged for Maria Butina - a Russian gun rights activist, who was jailed in the US in December 2018. She was deported back to Russia in October 2019.

David Whelan, meanwhile, has dismissed the allegations as nonsense.

"I can't imagine how someone with a law enforcement background who is also a former US Marine, and who is now working in corporate security and is also aware of the risks of travel, would have broken any law let alone the law related to espionage," he said.

Mr Whelan's friends in Russia, some with military connections like him, have also rebutted the charges of spying, all telling the BBC the idea was laughable.

In court in Moscow, he was nervous at first - but soon began speaking out to call himself a political hostage and denounce a 'kangaroo court'.

The BBC's Sarah Rainsford has followed Mr Whelan's case from the very start and interviewed him multiple times.

The last time they spoke by phone from prison, he told her he felt "abandoned" and "seriously betrayed" by the US government.

Left behind in previous prisoner swaps, he had grown despondent. Life in prison was tough, with guards waking him up multiple times to check he hadn't escaped.

Stuck serving a 16-year sentence, Mr Whelan said his parents were elderly, his beloved dog had died and his life was "slipping away" while the US government looked for a deal.

"Now that's finally happened," Rainsford writes. "Paul Whelan is going home and I suspect he himself can barely believe it."