Convicted Russian arms trafficker Viktor Bout was freed Thursday after he was traded for American basketball star Brittney Griner, who faced nine years in a Russian penal colony for a narcotics conviction.

According to media reports, Bout and Griner were exchanged on an airport tarmac in Abu Dhabi, the capital of the United Arab Emirates. The location was both pivotal and ironic. Bout, whose air transport empire at one point exceeded 60 Russian-built planes, had based many of his aircraft in the Emirates and lived there as well in the late 1990s and early 2000s at the height of his prominence as a weapons trafficker.

Griner, a WNBA basketball star and Olympic gold medalist, was serving a nine-year prison sentence after she was convicted by a Russian judge on narcotics charges. Last February, she was stopped at an airport near Moscow after customs officials found two vape cartridges containing hashish oil in her luggage.

American and Russian diplomats had negotiated for months after the U.S. offered to free Bout and send him back to Moscow in exchange for Griner and Paul Whelan, another American who had been imprisoned in Russia for the past four years. Neither country has openly provided details about the talks, but diplomatic sources have said that Moscow demanded the release of other Russians imprisoned in the West if Whelan was to be freed as well.

“While we celebrate Brittney’s release, Paul Whelan and his family continue to suffer needlessly,” U.S. Secretary of State Anthony J. Blinken said. “Despite our ceaseless efforts, the Russian Government has not yet been willing to bring a long overdue end to his wrongful detention.”

“This is a day we worked for a long time,” President Joe Biden said in remarks from the White House. Acknowledging the ordeal “has been hell” for Griner and her family, Biden said he had spoken to Griner after she was freed, adding: “She’s safe. She’s on a plane. She’s on her way home after months of being unjustly detained in Russia, held in intolerable circumstances.”

Bout was on his way by aircraft to Moscow, said Ivan Melnikov, a Russian lawyer who has handled cases of Russians held in the U.S. “Now he is flying home,” Mr. Melnikov said, adding that Mr. Bout’s wife, Alla, “is very excited. For her, this is a real New Year’s gift.”

Bout had been imprisoned in a medium-security federal prison in Marion, Ill. since 2012, when he was sentenced to 25 years behind bars after his 2011 conviction in a federal trial in New York. Bout was convicted by a federal jury on four counts, including conspiring to kill American citizens. Prosecutors said he had agreed to sell antiaircraft weapons to drug enforcement informants who were posing as arms buyers for the Revolutionary Armed Forces of Colombia.

Bout was brought to justice through a sting operation run by the Drug Enforcement Administration, which targeted Bout after more than a decade of flying weapons to warlords, militant groups and dictators from Afghanistan to Africa. Bout’s planes were even hired by American officials during the Bush administration to fly materiel in and out of Iraq after the U.S. invasion in 2002.

Until his 2008 arrest in Bangkok by DEA agents and Thai police, Bout evaded a succession of financial sanctions and arms embargoes aimed at him by the U.S., the United Nations and other Western nations. Former DEA and other federal officials were long alarmed by the prospect that Bout could be released, concerned that rogue nations and terror groups could target other Americans abroad in order to free international criminals extradited to the U.S.

During his federal trial in 2011, U.S. prosecutors alleged that Bout had been operating as an adjunct of Russian President Vladimir Putin’s government. An American informant testified that he met Bout in his office in a Russian military complex.

Bout had long been known as the “Merchant of Death,” a grim nickname tagged by a British minister who openly criticized Bout for his weapons deals in Third World nations.

“Merchant of Death” is also the title of the 2007 book co-authored by Douglas Farah and Stephen Braun that is the prime source of reportage on Bout’s rise and eventual fall as an international pariah.