Story highlights Pfc. Bradley Manning is accused in the largest leak of classified documents in U.S. history

In February, he pleaded guilty to 10 of the 22 charges against him

He did not plead guilty to the most serious charge -- that of aiding the United States' enemies

Manning's supporters rallied at Maryland's Fort Meade on Saturday

Supporters of Pfc. Bradley Manning, accused in the largest leak of classified documents in U.S. history, have adopted the phrase: "I am Bradley Manning."

But who is Manning? A whistle-blower? Or someone who aided the enemy in the midst of war?

Those and other questions go to trial Monday as Manning's court-martial is scheduled to begin at Maryland's Fort Meade.

He did not plead guilty to the most serious charge -- that of aiding the United States' enemies, which carries the potential for a life sentence.

During the proceeding, Manning spent more than an hour reading a statement that detailed why and how he sent classified material to WikiLeaks, a group that facilitates the anonymous leaking of secret information through its website.

Manning said he passed on information that "upset" or "disturbed" him but didn't give WikiLeaks anything he thought would harm the United States if it were made public.

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Photos: Key WikiLeaks figures in Manning trial Photos: Key WikiLeaks figures in Manning trial Key WikiLeaks figures in Manning trial – Army Pfc. Bradley Manning was convicted July 30 of stealing and disseminating 750,000 pages of classified documents and videos to WikiLeaks, and the counts against him included violations of the Espionage Act. He was found guilty of 20 of the 22 charges but acquitted of the most serious charge, aiding the enemy. He was sentenced to 35 years in prison. Hide Caption 1 of 5 Photos: Key WikiLeaks figures in Manning trial Key WikiLeaks figures in Manning trial – Before the court-martial began, Manning's attorney, David Coombs, thanked people for their support and fundraising efforts in "this important case." Hide Caption 2 of 5 Photos: Key WikiLeaks figures in Manning trial Key WikiLeaks figures in Manning trial – Former hacker Adrian Lamo turned Manning in to authorities. The Army private allegedly told Lamo about leaking the classified records. Hide Caption 3 of 5 Photos: Key WikiLeaks figures in Manning trial Key WikiLeaks figures in Manning trial – WikiLeaks founder Julian Assange fled to the Ecuadorian Embassy in London in June 2012 to avoid extradition to Sweden, where he is wanted for questioning over allegations that he raped one woman and sexually molested another. Assange has said he fears Sweden will transfer him to the United States, where he could face the death penalty for the work of WikiLeaks if he were charged or convicted of a crime. Manning has said he gave material to WikiLeaks after initially trying to contact The New York Times and The Washington Post. WikiLeaks has never confirmed that Manning was the source of its information. Hide Caption 4 of 5 Photos: Key WikiLeaks figures in Manning trial Key WikiLeaks figures in Manning trial – Daniel Domscheit-Berg, a longtime volunteer and spokesman for WikiLeaks, was considered to be Assange's closest collaborator. He quit WikiLeaks and said Assange's personality was distracting from the group's original mission. Domscheit-Berg went on to publish a tell-all book about the inner workings of WikiLeaks. He wrote that Assange evolved into a "paranoid, power-hungry, megalomaniac." Hide Caption 5 of 5

"I believed if the public was aware of the data, it would start a public debate of the wars," he told the court.

The U.S. military first detained Manning in May 2010 for leaking U.S. combat video -- including a U.S. helicopter gunship attack posted on WikiLeaks -- and classified State Department cables.

Manning was turned in by Adrian Lamo, a former hacker, whom Manning allegedly told about leaking the classified records.

In his statement to the court, Manning said he initially contacted The Washington Post and The New York Times to provide information.

He said he either wasn't taken seriously or got voice mail, so he gave the material to WikiLeaks.

WikiLeaks has never confirmed that Manning was the source of its information.

On Saturday, Manning's supporters rallied outside Fort Meade.

"People came from great distances to stand with a true American hero," said Jeff Paterson, director of the Bradley Manning Support Network.

"From Bradley's demeanor in court, it's clear he takes strength from the outpouring of support."

Manning was formally charged in February 2012.

On the eve of the court-martial, his lawyer, David Coombs, issued a rare public statement through his website.

He thanked those who raised money and awareness over the past three years, bringing "worldwide attention to this important case."