Ostracized by peers in Baghdad, busted for assaulting a fellow soldier and disdainful of the military's inattention to computer security, the 22-year-old intelligence analyst styled himself a "hactivist."
On Tuesday, the U.S. Army charged him with multiple counts of mishandling and leaking classified data and putting national security at risk.
Manning is suspected of leaking a classified video that shows a group of men walking down the street in Iraq before being repeatedly shot by Apache helicopters.
In a series of online chats in late May with a fellow computer geek, Manning claimed he had leaked a staggering 260,000 classified diplomatic reports, along with secret video of U.S. service members killing civilians, to the whistleblower website Wikileaks.org.
Whether or not Manning was the source, Wikileaks in April posted a video clips shot from a cockpit in 2007, of excited, laughing U.S. troops gunning down a group of men that included a Reuters news photographer and his driver. An internal military investigation concluded the troops acted appropriately, despite having mistaken camera equipment for weapons.
The case has drawn comparisons to Daniel Ellsberg's leak 40 years ago of the Pentagon Papers, a top-secret history of the Vietnam War. And it has bolstered perceptions that the Obama administration, despite a stated policy of open government, is as determined as its predecessors with keeping secrets.
Manning's online confidant, former outlaw computer hacker R. Adrian Lamo, reported their chats to U.S. authorities in late May, partly out of concern, he says, that national security was at stake.
Manning's military defense attorney, Capt. Paul R. Bouchard, didn't return calls and e-mails. The Army said Tuesday in a statement that a military version of a grand jury hearing will determine if Manning should face a trial by court-martial.
Manning is a slight, boyish-looking son of divorced parents from Crescent, Oklahoma, population 1,400. His Facebook page shows him smiling, with stylish, upswept hair and a stated affinity for gay-rights groups including Repeal the Ban, which seeks to end the "don't ask, don't tell" policy on homosexuals serving openly in the U.S. military.
Growing up in a house he shared with his parents and older sister, Manning had a sharp intellect and an interest in science, history and computers, said Jordan Davis, a boyhood pal. He said Manning also was determined at a young age to join the Army.
"It always seemed to me that Bradley was actually was more patriotic than probably even your average person," he said.
Chera Moore, another childhood friend, described Manning as highly intelligent and helpful. But she said he had "anger issues" and could get furious when people disagreed with him.
When Manning's parents split up in middle school, he left Oklahoma to live with his mother in Wales, Davis said.
After Manning graduated from high school and returned to Oklahoma, he quit or lost jobs in food service and retail in Tulsa, Davis said. Settling briefly in Chicago, Manning moved in with an aunt in Potomac, a Maryland suburb of Washington, D.C., and took community college courses before joining the Army in 2007.
Davis said Manning trained in Arizona, probably at Fort Huachuca, where he received instruction in compiling intelligence reports. Such reports help the military determine changes in enemy capabilities, vulnerabilities and probable courses of action.
In recent months, Davis said, Manning seemed to have grown more aware of social issues, including the gay-rights movement.
Manning's family members declined interview requests from The Associated Press.
According to partial chat logs Lamo shared first with Wired.com, Manning started communicating with Lamo on May 21, a couple of weeks after he was reduced in rank from specialist to private first class for assaulting another soldier.
In one of many personal asides, Manning told Lamo he had been the only nonreligious person in a town that had "more pews than people," and that he had custom-made dogtags reading "humanist."
Manning said he was pending discharge for an "adjustment disorder," according to the chat logs, but Army spokesman Lt. Col. Eric Bloom said Manning wasn't facing discharge when he was detained May 29.
The chats reveal Manning's frustration at being "regularly ignored" at work.
"I've been isolated so long," he wrote. "I just wanted to be nice, and live a normal life ... but events kept forcing me to figure out ways to survive ... smart enough to know what's going on, but helpless to do anything."
According to the chat logs, Manning's turning point came when he watched Iraqi police detain 15 people for printing anti-Iraqi literature that turned out to be a scholarly critique of Prime Minister Nouri al-Maliki.
"After that ... I saw things differently," he wrote. "I was actively involved in something that I was completely against."
Manning wrote he had copied onto compact discs "possibly the largest data spillage in American history" while listening and lip-synching to Lady Gaga's "Telephone." He wrote that he exploited "a perfect storm" of military computer vulnerability: "weak servers, weak logging, weak physical security, weak counterintelligence, inattentive signal analysis."
His motive, according to the chat logs: "I want people to see the truth ... because without information, you cannot make informed decisions as a public." Manning wrote that he hoped to provoke worldwide discussion, debates and reform, according to the chat logs.
Lamo told the AP he grew concerned "when it became apparent that he was leaking classified information to a foreign national" - Wikileaks' Australian founder Julian Assange. Early in their online conversations, Manning told Lamo that he had sent 260,000 State Department diplomatic cables to Wikileaks.
Lamo said he turned the chat logs over to Army criminal investigators after consulting with a friend who had worked in Army counterintelligence.
"It was a combination of an act of conscience and an act spurred by my understanding of the law," Lamo said. "I did this because I thought what he was doing was very dangerous."
Ellsberg said he considers Manning and Assange heroes for publicizing information the government wanted suppressed. He said Manning's alleged leak was possibly more significant than his own, which exposed the secret expansion of the Vietnam War.
"He is the first person in 39 years to do something comparable to what I did - and really better than what I did, because it's current," Ellsberg said.
Both Ellsberg and Gabriel Schoenfeld, an author who supports cracking down on leakers, said that the Obama administration has gone further than the Bush White House in pursuing alleged whistleblowers.
According to the charging document, Manning was charged with putting a classified video of a military operation recorded July 12, 2007, in Baghdad on his personal computer. That is the date and the location of the U.S. helicopter shooting. He was also accused of accessing more than 150,000 classified State Department cables.
While the charging document didn't mention Wikileaks, Manning was accused of giving the video and at least one cable "to a person not entitled to receive" them. That cable was titled "Reykjavik 13." Wikileaks has posted a Jan. 13 cable about a meeting in Reykjavik, Iceland, summarizing U.S. Embassy discussions with Icelandic officials about the country's financial troubles.
The charges against Manning follow April's indictment of former National Security Agency worker Thomas Drake for allegedly lying and obstructing justice in an investigation of classified information leaks to The Baltimore Sun.
The Army's decision to charge Manning also followed a federal grand jury's reissuance in April of a subpoena seeking the names of some sources for journalist James Risen's book, "State of War: The Secret History of the CIA and the Bush Administration."
Schoenfeld, author of "Necessary Secrets" and a senior fellow at the conservative Hudson Institute, said leaks of military information during wartime run counter to America's interests.
"We're serious about trying to win, and it's extremely damaging to the morale of our troops," he said. "It inflames the local opinion, where we have a real battle for hearts and minds."