(CNN) -- Controversial whistleblower Julian Assange was "a very bright boy with a keen sense of right and wrong" when he was growing up, according to his stepfather.
The young Assange grew up constantly on the move, the son of parents who were in the theater business in Australia.
Brett Assange, who now lives alone in Sydney, was Julian's first real dad, raising him from the age of one and giving him his surname.
In an exclusive interview with CNN affiliate Seven News, he described his stepson as a "sharp kid who always fought for the underdog."
He added: "Strangely enough I always thought he would do something like this. He was always very independent. And he certainly wouldn't take no for an answer.
"He always stood up for the underdog. I remember that, like with his school friends. He was always very angry about people ganging up on other people. He had a really good sense of equality and equity."
Now age 39, Julian Assange faces his toughest challenge yet, as he sits in a British jail fighting Swedish attempts to extradite him in relation to a sex crimes investigation.
This comes as his Web site, WikiLeaks, has been releasing reams of classified U.S. intelligence, prompting politicians and power-players the world over to call for his arrest for exposing sensitive documents. Supporters contend Assange represents free speech at its finest. They say he is a man and an organization committed to outing injustices.
Yet despite unrelenting global media attention, Assange has remained an enigmatic figure. Perhaps that's because he learned as a child to cope with living a solitary life.
Assange has been described by his mother, Christine, as "highly intelligent."
He was just 16 when she bought him a Commodore 64 computer. It was 1987, and there were no Web sites. Assange attached a modem to his computer and began his journey through the growing world of computer networks.
"It's like chess," he told New Yorker magazine. "Chess is very austere in that you don't have many rules, there is no randomness and the problem is very hard."
Though his mother raised him without any religious influence, she sensed that from a tender age, her son was led by a strong desire to do what he perceived as just.
"He was a lovely boy, very sensitive, good with animals, quiet and has a wicked sense of humor," she told the Melbourne, Australia, Herald Sun newspaper Wednesday.
He would go on to study mathematics and physics at the University of Melbourne.
In interviews, his scientific precision shines through. He speaks in a baritone voice, in measured pace, choosing each word carefully. He can be charming yet cagey about his private life and is rarely shaken by discussions of even the most controversial revelations on WikiLeaks.
He's the kind of person who, he says, can hack into the most sophisticated computer system. But he can forget to show up for an interview. Or cancel at the last minute.
When he talks, he displays an astonishing breadth of interests: from computers to literature to his travels in Africa.
Even when he walked out of a CNN interview in October after refusing to answer questions about the sex charges in Sweden, Assange remained cool and collected. He projected a stately demeanor helped by his profusion of gray hair -- which grew at an early age -- and an equally steely facial expression.
After his initial foray into computers, Assange delved into computer encryption and grew keen on computer security. He once relayed a story about how he set up an encryption puzzle based on the manipulation of prime numbers.
The New Yorker article, published earlier this year, described how in 1991, Assange hacked into the master terminal of the telecom company Nortel, after which he developed a growing fear of arrest.
He had married and fathered a child when he was only 18 but the relationship fell apart and his wife left him with their infant son.
He was charged with 31 counts of hacking in Australia but in the end paid only a small sum in damages, according to the New Yorker.
The young hacker began to focus his attention away from network flaws to what he perceived as wrongdoings of governments.
In a 2007 blog post on IQ.org, he wrote:
"The whole universe or the structure that perceives it is a worthy opponent, but try as I may I can not escape the sound of suffering. Perhaps as an old man I will take great comfort in pottering around in a lab and gently talking to students in the summer evening and will accept suffering with insouciance. But not now; men in their prime, if they have convictions are tasked to act on them."
IQ.org is believed to be a blog created by Assange and is registered under the name "JA" by the same U.S. domain company as WikiLeaks. Its Australian postal address is also the same as a submissions address for WikiLeaks.
Among myriad topics addressed in the blog, Assange discusses mathematics versus philosophy, the death of author Kurt Vonnegut, censorship in Iran and the corporation as a nation state.
Driven by the conviction of an activist and the curiosity of a journalist, Assange founded WikiLeaks in 2006. He slept little and sometimes forgot to eat. He hired staff and enlisted the help of volunteers.
Always, he protected his sources, never discussing where information came from.
"People should understand that WikiLeaks has proven to be arguably the most trustworthy new source that exists, because we publish primary source material and analysis based on that primary source material," Assange told CNN. "Other organizations, with some exceptions, simply are not trustworthy."
The Web site skyrocketed to notoriety in July when it published 90,000 secret documents about the war in Afghanistan. It was considered the largest intelligence leak in U.S. history.
WikiLeaks followed in October with classified documents about the Iraq war. And then this week, it began posting 250,000 cables revealing a trove of secret diplomatic information.
Some praised WikiLeaks as a beacon of free speech. But others, including outraged Pentagon and White House officials, consider it irresponsible and want WikiLeaks silenced for what they call irreparable damage to global security.
Assange, the elusive public face of WikiLeaks, catapulted to celebrity status.
The image of the lean, lanky, leather jacket-clad figure with the pale skin and mop of white hair was splashed on television screens and websites. Everyone wanted to know how the editor in chief of WikiLeaks had pulled it off.
Time magazine has nominated him for its Person of the Year, calling him a "new kind of whistle-blower ... for the digital age."
But Assange's notoriety did not stop there. Shortly after the Afghan war releases, he became the subject of a sex crime case in Sweden.
The Stockholm Criminal Court issued an international arrest warrant for Assange two weeks ago on probable cause in that case, saying he is suspected of rape, sexual molestation and illegal use of force in separate incidents in August. He could be sentenced to two years in prison if convicted.
Interpol issued a high alert for Assange on Wednesday at the request of Sweden.
Assange has maintained his innocence and called the charges in Sweden a smear campaign. He has also dismissed reports of internal strife within WikiLeaks.
Daniel Domscheit-Berg, a longtime volunteer and spokesman for WikiLeaks who recently quit his job, told CNN that Assange's personality was distracting from the group's original mission: to publish small leaks, not just huge, splashy ones like the Afghan War Diary.
Assange took issue.
"It is my role to be the lightning rod," Assange said. "That is a difficult role. On the other hand, I get undue credit."
Assange's mother said Wednesday that she feared her son had become "too smart for himself."
"I'm concerned it's gotten too big and the forces that he's challenging are too big," Christine Assange told the Herald Sun.
She did not comment on the sex crimes charges in Sweden. But she said lately, Assange had distanced himself from his family to protect them.
Assange, too, declined to address the charges in the October interview with CNN in London.
"This interview is about something else. I will have to walk if you are ... going to contaminate this extremely serious interview with questions about my personal life," he said.
Then, he pulled off his mic, said sorry, and walked away.
CNN's Mia Aquino, Atika Shubert, Ashley Fantz, Moni Basu and Paul Armstrong contributed to this report.