From a swivel chair and a small desk in a military courtroom in Maryland, Bradley Manning has for more than a year heard US government lawyers outline why he should spend the rest of his life in jail.

By recently admitting he was the source of thousands of secret US diplomatic cables and war logs regarding Afghanistan and Iraq, later published by WikiLeaks, he appears certain to be found guilty at a trial beginning Monday.

But having denied the most serious charge of "aiding the enemy," chiefly Al-Qaeda, the man accused of causing his country's worst ever security breach remains an enigma: a hero to his followers, an enemy of the state to others.

The short, skinny, bespectacled US Army private has cut a confident figure in previous court appearances, exuding an outer calmness and quiet resolve on the occasions that he has testified and answered questions.

His demeanor belies evidence of numerous episodes of suicidal tendencies and erratic behavior, such as licking the bars of his cell during some of the 1,109 days he has spent in military detention.

Born in Crescent, Oklahoma to an American father and a Welsh mother who later divorced, Manning had an aptitude for computers from an early age and reportedly created his first website when he was only 10 years old.

At the age of 17, by when he was living as an openly gay man, Manning got a job with a software company in Oklahoma City, only to be fired four months later.

He then migrated to computer hacking, attending events filled with other hackers, a paradoxical prelude to the high-level security clearance he obtained when he became a military intelligence analyst in a warzone.

"I am the type of person who always wants to figure out how things work. And as an analyst, this always means I want to figure out the truth," Manning said in his pre-trial testimony at the Fort Meade military base near Washington.

His homosexuality and gender identity issues -- Manning enlisted despite the "Don't Ask, Don't Tell" policy on gays in the military at the time -- led to problems. As at school, peers bullied and ridiculed him.

Commanders judged him ill-suited to military life and during training, he was recommended for discharge. But his technical skills were perfectly suited to becoming an intelligence analyst and the decision was overturned.

Ultimately, he was sent to Iraq where -- appalled with what he saw in the reports he analyzed -- his motivation for illicitly uploading such material and passing it to WikiLeaks appears to have taken hold.

The US Army video recording of two Apache attack helicopters gunning down a group of Iraqis in Baghdad, an attack that killed at least 12 men and wounded two children, was an incident Manning said "burdens me emotionally."

"They dehumanized the individuals they were engaging and seemed to not value human life by referring to them as 'dead bastards' and congratulating themselves on their ability to kill in large numbers," Manning said in court.

Such an account matches the view of Manning supporters who say he is a voice of conscience who lifted a veil on what he considered the worst transgressions of US foreign policy, by its political and military leaders.

Daniel Ellsberg, the US military analyst who leaked the Pentagon Papers, a top secret study regarding decision-making in relation to the Vietnam War, has said Manning is a hero who should be awarded the Nobel Peace Prize.

The Bradley Manning Support Network has received more than $1.1 million in donations to pay his legal costs and has campaigned relentlessly on his behalf.

But many people disagree with the cause, most notably Adrian Lamo, the fellow hacker who turned Manning over to the authorities after reading the soldier's innermost thoughts from Iraq during Internet messaging discussions.

"What I saw in those chats was an admission of acts so egregious that it required that response," Lamo told a pre-trial hearing of taking the decision that ultimately landed Manning in the dock.