Viktor Bout: Who is the Merchant of Death

Viktor Bout, one of the world's most infamous arms dealers, has been released from US custody as part of a prisoner exchange with US basketball star Brittney Griner.

Griner had been in custody since February after Moscow airport officials found cannabis oil in her luggage while she was returning to the US after playing in Russia.

Rumours had circulated in US media for months that senior state department officials had sought to secure Griner's release in exchange for the arms dealer's freedom.

So notorious are the exploits of the former Soviet air force officer that they inspired a Hollywood film, and garnered him an impressively fearsome nickname.

But who is the man known as the Merchant of Death?

Bout was extradited from Thailand to the US in 2010, after a sting operation by the US Drug Enforcement Agency (DEA) two years earlier.

Agents from the DEA posed as potential buyers from the Revolutionary Armed Forces of Colombia, known as Farc. That group - which has since disbanded - was classified as a terrorist organisation by the United States.

Bout claimed he was simply an entrepreneur with a legitimate international transport business, wrongly accused of trying to arm South American rebels - the victims of US political machinations.

But a jury in New York didn't believe his story.

He was sentenced to 25 years in prison in April 2012 after being found guilty of conspiracy to kill Americans and US officials, delivering anti-aircraft missiles and aiding a terrorist organisation.

His three-week trial heard that Bout had been told the weapons would be used to kill US pilots working with Colombian officials. Prosecutors said he replied: "We have the same enemy."

Bout - a Russian national born in Soviet-ruled Tajikistan - began his career in air transport in the early 1990s, after the fall of the USSR.

According to a 2007 book - Merchant of Death, by security experts Douglas Farah and Stephen Braun - Bout built up his business using military planes left on the airfields of the collapsing Soviet empire in the early 1990s.

The sturdy Antonovs and Ilyushins were up for sale along with their crews, and were perfect for delivering goods to bumpy wartime airstrips around the world.

Bout - who was 45 when he was sentenced - is said to have begun channelling weapons through a series of front companies to war-torn parts of Africa.

The UN named him as an associate of former Liberian President Charles Taylor - who was convicted in 2012 on charges of aiding and abetting war crimes during the Sierra Leone civil war.

"[Bout is a] businessman, dealer and transporter of weapons and minerals [who] supported former President Taylor's regime in [an] effort to destabilise Sierra Leone and gain illicit access to diamonds," UN documents state.

Media reports in the Middle East claimed he was a gun-runner for al-Qaeda and the Taliban.

He is also alleged to have armed both sides in Angola's civil war and supplied weapons to warlords and governments from the Central African Republic and the Democratic Republic of Congo to Sudan and Libya.

In an interview with the UK's Channel 4 News in 2009, he flatly denied ever dealing with al-Qaeda or the Taliban.

But he did admit to flying arms to Afghanistan in the mid-1990s, saying they were used by commanders fighting against the Taliban.

He also claimed to have helped the French government transport goods to Rwanda after the genocide, and to have transported UN peacekeepers.

But law enforcement agencies pursued him throughout the 2000s. He left his home in Belgium in 2002 when the authorities there issued an arrest warrant.

It is thought Bout travelled under several aliases, moving through countries such as the United Arab Emirates and South Africa before resurfacing in Russia in 2003.

In the same year, British Foreign Office minister Peter Hain coined the nickname Merchant of Death

After reading a 2003 report about him, Mr Hain said: "Bout is the leading merchant of death who is the principal conduit for planes and supply routes that take arms... from East Europe, principally Bulgaria, Moldova and Ukraine to Liberia and Angola.

"The UN has exposed Bout as the centre of a spider's web of shady arms dealers, diamond brokers and other operatives, sustaining the wars."

The US made moves against Bout throughout the 2000s, freezing his assets in 2006, but there was no law he could be prosecuted under in the US.

Instead, US agents bided their time until 2008 when they posed as buyers for Colombia's Farc rebels and gained an introduction to Bout through one of his former associates.

Shortly after the undercover officers discussed arms shipments to Farc with Bout, Thai authorities arrested him and lengthy legal proceedings began to bring him to the US.

Bout said the US case against him was politically motivated; his wife has been quoted as saying his only connection with Colombia was "tango lessons".

The Russian authorities supported him throughout his legal proceedings, with Foreign Minister Sergei Lavrov vowing to fight to secure his return to Russia and labelling the Thai court's decision "unjust and political".

The 2005 film Lord of War, loosely based on the arms dealer's life, has the anti-hero escaping justice at the end.

But such an ending eluded Bout, who had remained in prison in the US since his conviction in 2012.