Viktor Bout, the notorious Russian gun dealer dubbed the "Merchant of Death," was released from a U.S. prison Thursday (Dec. 8) in exchange for Olympian and WNBA star Brittney Griner.

A Former Soviet military linguist Bout, 55, was sentenced to 25 years in prison for conspiring to kill Americans, obtaining and exporting anti-aircraft missiles, and giving financial assistance to a terrorist group. Bout insisted he is innocent, and the Kremlin has repeatedly called his prosecution in the U.S. "baseless and biased." But government officials in America and Europe regarded him as one of the world’s most prolific arms dealers.

U.S. State Department officials emphasized in comments to reporters that the trade was a one-for-one exchange. Paul Whelan, a former U.S. Marine still imprisoned in Russia was never part of the negotiation, although the United States continues to work for his release.

Bout had been detained in the U.S. Penitentiary Marion, a medium security federal prison in Illinois. Federal Bureau of Prisons records show his release date had been set for August 19, 2029. Former Attorney General Eric Holder, who served in the Obama Administration, once called him, “one of the world’s most prolific arms dealers.” His penchant for arms dealing inspired the 2005 film “Lord of War,” starring Nicholas Cage as a character based on him.

Published reports say he started his own cargo airline, Air Cess, with a modest fleet of Russian aircraft that transported cargo to Africa and Afghanistan in 1995, when he was 28.

In the years that followed, Bout supplied more advanced weapons, sometimes to both sides of the violent battles, and aided in igniting civil wars all over the world. His dealings had a tremendous impact in African conflicts.

According to Africanarguments.org, among those he is said to have supplied arms to include Liberian dictator Charles Taylor, the Northern Alliance as well as the Taliban in Afghanistan, fighters in the Balkans, and both sides of the Angolan conflict – the government and Jonas Savimbi’s UNITA rebels.

In 2007, the Drug Enforcement Administration came up with a scheme to get Bout out of Russia by tempting him with an arms trade, according to CBS News. An undercover agent spoke with Bout's business partner about a business venture. This set up an encounter between Bout and the DEA's fake arms buyers, who were impersonating representatives of the FARC, the Revolutionary Armed Forces of Colombia.

Bout's associate returned to Russia to present the deal to him. It worked.

In 2008, thinking he was on his way to meet Colombian rebels in Thailand to discuss shopping what prosecutors said was "an arsenal of military grade weapons" to attack American helicopters in Colombia, Bout told the DEA informants posing as FARC officials he could airdrop weapons in Colombia and that those arms could be used to kill Americans. This admission prompted the Thai police and DEA agents listening in to the meeting to burst into the room and arrest Bout.

After two years of legal proceedings, he was extradited to the US in 2010, and a year later he was found guilty on terrorism charges. Preet Bharara, then-U.S. Attorney in Manhattan said in a statement after his trial that Bout was “ready to sell a weapons arsenal that would be the envy of some small countries. He aimed to sell those weapons to terrorists for the purpose of killing Americans.”

With the prisoner swap in exchange for Griner, he is now free again. It is unclear what his plans are. But he has always maintained that he is only a businessman, not an arms dealer. There is some concern from the Pentagon that Bout could return to arms trafficking, particularly at a time when Russia is waging war in Ukraine

“We cannot ignore that releasing Bout back into the world is a deeply disturbing decision,” Sen. Bob Menendez, chair of the Senate Foreign Relations Committee said in a statement Thursday, according to Politico. “We must stop inviting dictatorial and rogue regimes to use Americans overseas as bargaining chips, and we must try do better at encouraging American citizens against traveling to places like Russia where they are primary targets for this type of unlawful detention.”