Scanning back over daily flight logs on his computer, Walker—a trim, unflappable longtime Air National Guard officer—bristled each time the name of Bout's flagship air firm, Irbis, popped up on manifests from the central U.S. air command base in Qatar. The 37-year-old Russian had somehow pulled off an astonishing metamorphosis: from hunted international criminal—in the same league as Osama bin Laden—to secret delivery man for the Pentagon. For years, U.S. officials had been tracking Bout in an effort to ground his vast air transport enterprise, which flooded the world's killing fields throughout the nineties with endless shipments of everything from black-market AK-47s to massive helicopter gunships and fueled the bloody slaughter of tens of thousands. But now that same logistical prowess—a durable armada of 60 planes that could also carry legitimate freight such as food or humanitarian supplies—made Bout's network vital to U.S. troops in Iraq.

Every year for the past decade, as many as 500,000 people have been killed in sputtering, obscure regional wars that have eroded international stability from Congo to Colombia—most of them with portable assault rifles such as the AK-47. The profligate use of Russian-designed weapons and ammo creates a constant demand for resupply, and Bout has armed almost every warlord and militant who can afford it. He was the single largest supplier of guns to the Revolutionary United Front and its child soldiers in Sierra Leone, stoking horrific campaigns of mass torture, rape, and amputation. Bout also armed warring factions in Afghanistan in the late nineties, nimbly working for the Northern Alliance government while covertly selling planes and weapons to Taliban militants, who shared them with Al Qaeda. Whereas rival international gunrunners provided merely the arms and the false documents authorizing their transfer, Bout alone offered a full-service package, including the planes that could deliver them to the riskiest war zone. As a result, the paunchy, flint-eyed ex–Soviet military officer with a drooping brush mustache—who inspired the 2005 Nicolas Cage film Lord of War—has made hundreds of millions of dollars and remains the most lethal figure in the global arms trade.

Walker soon realized that the Pentagon faced an acute public relations problem. Irbis, which based its planes in Sharjah, United Arab Emirates, had been hired as a secondary military subcontractor, delivering essential supplies such as tents and food for American firms working for the U.S. Army and the Marines. Other firms linked to Bout had even carried high-security items like guns, ammo, and armored vehicles. In addition, Irbis was a contractor for Federal Express under an arrangement with the Dubai-based Falcon Express Cargo Airlines. And Irbis was also flying, Walker learned, under reconstruction contracts with Kellogg, Brown and Root (KBR), a subsidiary of Halliburton, the famous conglomerate once headed by Vice President Dick Cheney. (KBR denied knowledge of the flights, while FedEx blamed Falcon Express.)

As Bout expanded his operation, he hired the castoffs of Russia's eviscerated air force and arms industry, building a loyal outfit of 350 employees that included daredevil pilots, ground crews adept at keeping the decaying planes aloft, weapons suppliers, financial advisers, and even a gem expert who flew along on African sorties to inspect the blood diamonds Bout was sometimes paid with. "His structure is a lot like what we see in drug cartels," notes a U.S. Treasury official. Thriving on financial guile, Bout has scattered shell companies around the world that can be launched, renamed, and discarded at a moment's notice, with planes disguised by fake registries and tail numbers. Arms flights are his specialty, but Bout also caters to his clients' recreational needs. One evening during a 2001 tour of the Congolese hills, Jean-Pierre Bemba—a warlord leading a rebel army of guerrillas and gun-toting teenagers—was camped on a remote mountaintop when he and his crew realized that they were low on beer. As part of his all-inclusive modus operandi, Bout had rented Bemba two Soviet-built Mi-24 helicopters. Moving with the authority of a seasoned commando, Bout gathered his men and, accompanied by a heavily armed escort of 20 soldiers, choppered across Lake Albert into Uganda. There they raided a small Ugandan town, ordered residents in the market square to find all the available beer, and flew back to Congo, fortified with enough drink to last the night.

Roaming war zones as a capitalist convert in golf clothes, Bout did business with the third world's cruelest strongmen. His catalog of munitions—rifles, land mines, surface-to-air missiles, and tanks pilfered from poorly secured ex-Soviet storerooms—helped sustain the regimes of Charles Taylor in Liberia and Mobuto Sese Seko in Zaire (now Congo), and fueled the rebel campaigns of Bemba in Congo, Jonas Savimbi in Angola, Paul Kagame in Rwanda, and Sam "Mosquito" Bockarie in Sierra Leone. But what also alarmed U.S. officials at the time—and to this day—was the potential that Bout's planes could carry even more dangerous cargo, such as nuclear material. "We paid particular attention to the WMD issue because of Bout's connections inside the Soviet military," says Michael Scheuer, a former CIA analyst who headed Alec Station, the agency's in-house unit that tracked bin Laden in the late nineties. U.S. counterterror officials knew that bin Laden's Al Qaeda lieutenants had already tried and failed in the early nineties to buy nuclear materials in Sudan, and they were anxious about the Eastern bloc's loose grip on Soviet nukes and radioactive substances. Unlike his competitors—such as the Odessan Leonid Minin, whose weapons trafficking to Liberia in the late nineties ended in his brief incarceration in a Milan jail—Bout had the ideological neutrality and elaborate infrastructure to deliver the goods, making him a new type of transnational threat.

As he amassed his fortune, Bout developed the glowering countenance of a commissar and gained a reputation for being brash, even bullying. During his 2001 tour with Bemba, someone mentioned a biblical verse with an interpretation that seemed to bother the Russian. In front of a crowd of people, Bout—a gifted linguist who speaks fluent English, French, and Spanish—suddenly launched into a loud, extended discourse in French explaining how the verse should be taken and how foolish the interpreter was, stunning the audience into silence. He also lectured Liberia's Charles Taylor like a schoolboy and thought nothing of keeping a coiled killer like Mosquito Bockarie waiting at a Monrovia roadblock. Bout was just as relentless in taking on the freebooting Russian airmen who competed with him. In one celebrated case, his operation boldly spirited away a decrepit Ilyushin plane that had been consigned for use as a Soviet war monument. Former Russian aviation official Valery Spurnov recounted a tale of Bout offering one of his pilots $20,000 to fly a shuddering wreck out to a desert landing in the Emirates, where it was promptly turned into a highway-side billboard. "It was as if he was walking on the edge of the knife all the time," recalls his ex-partner Alexander Sidorenko, a decorated paratrooper who parted ways with Bout in the early nineties. Of course, Bout's hauteur was bolstered by his constant security detail of heavily armed Russians who had served with the special forces of the GRU.

The numbers were staggering. Irbis and its alter-ego air firm, Air Bas, accounted for hundreds of Iraq flights during 2003 and 2004, sluicing millions of dollars into Bout's coffers. One air transporter with extensive supply work in Baghdad estimates that Bout's planes made as many as 1,000 flights into Baghdad International Airport and other Iraqi airfields by the end of 2004. And fueling records later released by the U.S. Defense Logistics Agency reveal that Irbis planes refueled at American facilities in Baghdad 142 times between March and August 2004, indicating an almost daily pace of flights into Iraq. At $60,000 per flight, U.S. taxpayers may have contributed as much as $60 million to Viktor Bout's business.

With diplomatic outrage mounting, President George W. Bush finally signed a Treasury order in July 2004 that authorized the permanent freezing of Bout's assets in or passing through U.S. banks and called him an "unusual and extraordinary threat to the foreign policy of the United States." But the Russian's planes continued to fly for American contractors in Iraq for more than a year. (Moreover, a second order in 2005 targeting 30 of Bout's quasi-legitimate companies was quietly delayed at the request of U.S. Central Command officials in order to allow Bout's planes to finish their Iraq deliveries.) While he had hubs in Belgium, Central Asia, and the United Arab Emirates, Bout himself lived openly in Russia the whole time. For years he traveled easily among lavish homes from Belgium to South Africa, but whenever foreign pursuers began to turn up the pressure, he retreated to the safety of his well-appointed residences in Moscow and St. Petersburg, where his wife and young daughter lived.

"It's contrary to a smart war on terror," says former National Security Council deputy Gayle Smith, who was involved in the Clinton administration's earlier effort to arrest Bout. "Even if you needed a cut-out to transport supplies, why would you go to the one on the bottom of the pile, with the most blood on his hands?" Evidently the Defense Department had failed to scrutinize lower-level subcontractors during the feverish run-up to war—or even to compile a watch list of dubious companies. "It was dealing with the devil to get what needed to be done, and the powers that be approved it," says Walker. "If the government really wanted him bad, they could have come up with a pretext and seized his planes. But they looked at Viktor Bout and figured, this guy's an asshole, but he's our asshole, so let's keep him in business."

The most official of the array of passports belonging to Viktor Anatolijevitch Bout pinpoints his birthplace in the faded Soviet outpost of Dushanbe, Tajikistan, a Central Asian capital hemmed in by mountains and sunken in rural poverty. Bout has acknowledged graduating from Moscow's Military Institute of Foreign Languages—well known among U.S. military intelligence officials as a feeder academy for the Soviet espionage services—but has strenuously denied any KGB background. Moving swiftly in the nation's struggling new capitalist society during the nineties, he began acquiring planes destined for the scrap heap, including a trio of old Antonovs—Soviet-made cargo planes that could carry upward of 20 tons—for $40,000 apiece. According to Bout associates, his senior contacts in the GRU—the secretive Soviet military intelligence network—were critical for his start-up, and his initial flights carried weapons to approved third world clients.

Bout displayed a tender side only to his intimates. At some point around the early nineties he married an aspiring businesswoman named Alla, reportedly the daughter of an ex–KGB agent. In 1994 Alla gave birth to a daughter, Elizabeth, and Bout soon moved the family to South Africa to provide a more stable home environment. But he remained in transit, talking in code every day on satellite phones to stay ahead of eavesdropping intelligence agents. On the rare instances when he spoke to the press about his business, he steadfastly denied any criminal association. (Bout's Moscow-based lawyer, Victor Burobin, did not respond to detailed questions.) "I exclusively deal with air transportation," Bout said in a 2002 radio interview, insisting that his payloads were "regulated not by the owner of the transport but by that organization that undertakes the transportation." Bout's brother and closest business confidant, Sergei, put it more bluntly: "I am a taxi driver; I am a carrier. I don't know what I carry. Maybe I carry a nuclear bomb. No one is informing me about it."

During the last years of the Clinton White House, a small circle of officials—well aware that Bout's air fleet and global infrastructure rivaled those of many NATO nations—targeted Bout for arrest, but the effort petered out in the first months of the Bush administration. In an attempt to kick-start momentum, a member of the Bout chase team decided to host a Viktor Bout party in the spring of 2001 to acquaint people from the CIA and the NSC. Several dozen officials, along with their spouses and children, turned up for the gathering, which took place under the cover of a weekend cookout in the Virginia suburbs south of Washington, D.C. As the burgers and hot dogs sizzled in the fading light, guests clustered into small groups to discuss the latest developments in their hunt for the elusive arms trafficker. "The idea of 30 or 40 people showing up on this one issue was remarkable," says one attendee. "Our spouses had no idea why we were there, but there would be little cliques of people off in the corner who talked about Bout. It was fun." The officials were focused mostly on the Bout organization's uninterrupted flow of arms to African despots and the Taliban—not to mention the worst-case possibility that Bout might help deliver a nuke to terrorists. Soon thereafter, Lee Wolosky, the top NSC official leading the effort to nab Bout, briefed Condoleezza Rice's national security team and scheduled a pre–presidential briefing meeting for September 11, 2001. In the chaos of the morning's events, the hunt for Viktor Bout was essentially lost, buried in the rubble of 9/11.

Naturally, Bout found a way to cash in on the catastrophic attacks. European intelligence officials suspect that just a month later, his aircraft may have transported U.S. Special Forces and the CIA into Afghanistan. His pilots had been flying into Taliban territory for the past five years and were familiar with the safest routes and most obscure landing strips. "We know Bout had his aircraft near Afghanistan and made them available to the U.S. efforts almost immediately," says one European official. "They needed him and he had the only airlift capacity in the region. The deal was that if he flew, the U.S. would leave him alone." Richard Chichakli, one of Bout's business aides, would later boast that Bout organized three flights ferrying U.S. personnel to Afghanistan. "Bout could not have done what he did without the help of princes, kings, and presidents," says Michael Scheuer.

Some European officials warily suggest that the U.S. has even helped Bout evade arrest. On February 18, 2002, the Belgian Foreign Ministry issued an international Red Notice through Interpol accusing Bout of laundering $32.5 million in arms-trafficking earnings between 1994 and 2001. The notice required officials in any country where he was spotted to apprehend him and turn him over to Belgian authorities. As the alert circulated around the world, European intelligence agents developed solid information that Bout was going to be flying to Greece from one of his new hubs in Moldova. As soon as Bout's plane took off, British agents sent an encrypted message notifying superiors in London to prepare for his imminent arrest in Athens. But shortly after the message was sent, the aircraft suddenly veered off its flight plan and disappeared in mountainous terrain. About 90 minutes later the plane reappeared on radar screens, and when it landed in Athens, Greek and British special forces stormed the aircraft, only to find it empty except for the pilots and a few passengers. Bout was spotted in Congo less than 24 hours later, and eventually he returned to safety in Moscow, where he is protected by powerful officials and crime bosses. It remains the closest he has ever come to being caught. "There were only two intelligence services that could have decrypted the British transmission in so short a time," says one European intelligence official familiar with the operation. "The Russians and the Americans. And we know for sure it was not the Russians."

A small band of European intelligence officers was authorized to try and nab Bout again during a visit he planned to Madrid in March 2004. But on March 11, an Al Qaeda–affiliated terror group set off bomb attacks on the city's train system, killing 191 people and wounding thousands of others. Bout canceled the trip. "It was a very good plan—we would have had him," says one operative involved.

These days, international initiatives to hunt down Bout have been mostly abandoned, confined to sporadic efforts by the U.N. and Treasury Department to freeze his assets. The CIA no longer has analysts specifically assigned to monitor his flights and follow his activities. "They're all working on counterterrorism now," says a U.S. official. Ironically, just as the Clinton administration struggled to come to terms with the threat posed by bin Laden, the Bush White House has been too preoccupied with bin Laden to confront the grave multi-front danger hiding in plain sight. Russian president Vladimir Putin, for his part, has never commented directly on Bout to the Western press—and the U.S. has not pressed him—but in 2002, soon after the Belgian laundering indictment, the Kremlin declared that "there is no reason to believe that this Russian citizen has committed any illegal actions."

According to intelligence sources who have followed his activities for years, Bout is living in a luxury apartment complex in Moscow, where he is occasionally spotted eating at the upscale sushi bars he favors. He often shows up at the offices of Isotrex, a semi-official foreign trade firm allegedly directed by a group of deputy ministers tied to the nation's armament manufacturers. In general, he still moves with ease across Russia and the Eastern bloc, ranging from his home base to satellite outposts in Moldova, Belgium, and Kazakhstan and arms depots in Bulgaria and Ukraine. Outside Eastern Europe, the U.N. travel ban forces him to travel mostly by land, relying on shifting passports. "He is out there, still doing his deadly business," sighs an intelligence official who once specialized in Bout's operation.

In fact, there is growing evidence that in the past few months, Bout has returned to his stock-in-trade. U.S. intelligence sources strongly suspect that last summer Bout's planes flew weapons and supplies to the radical Islamic Courts Union that briefly seized power in Somalia and continues to destabilize the capital of Mogadishu and outlying areas. Bout was also reportedly sighted at a Hezbollah-controlled building in Beirut while the Lebanese terrorist organization—armed with a cornucopia of late-model Russian and Eastern European rockets and weapons—faced off with Israeli troops last year. Beyond his roles in those emerging crises, Bout remains a WMD threat because of his logistical reach throughout Africa, Central Asia, and the Mideast, and because he will play accomplice to even the most dangerous customer for the right price. Most ominous of all, though, is that despite Bout's mercenary habit of arming Al Qaeda's allies in the past, the U.S. is doing little to prevent him from going even further in the future .