To Chung bought his first apartment in New York before he hit 25. It was not hard, not when he was armed with degrees from Columbia and Harvard, and worked as an investment banker.

But when he was 32, he gave up his nice pay cheque, business-class travel and other perks to help children in China orphaned or affected by HIV, the human immunodeficiency virus that causes Aids.

Over the last two decades, he and the Chi Heng Foundation (CHF) - a non-governmental organisation (NGO) he founded - have sponsored the education of 20,000 children impacted by HIV in China. More than 3,000 of them have made it to university.

Now 50, he has no regrets about giving up the high life.

"The world can do with one less banker. But these children need help. If I didn't help them, they wouldn't be able to go to school," says Mr To, who was in Singapore last month to explore plans to set up a local office for Chi Heng. The charity, which has 13 offices in Hong Kong and China, also fights discrimination against people with HIV and funds initiatives in Aids prevention and care.

Mild-mannered and earnest, the elder of two children was born in Hong Kong to a businessman and his wife.

When he was nine, his parents divorced.

"I felt lost, but I also became very independent," he says.

At 14, he left Hong Kong to live in San Francisco with his father.

"I arrived in San Francisco when Aids was making headlines every day. There was a lot of panic and social stigma," he recalls.

"As a teenager and a new immigrant, you get affected. It was like living in Hong Kong during the Sars epidemic, or in West Africa during the Ebola outbreak."

Aids took on an even more personal face when his high school maths teacher died of the disease.

"It suddenly was no longer just something I read about in the newspapers. It happened to someone I was close to," he says.

There was, however, no fear. He read up all he could about the disease. "I became aware of the discrimination and sensitive to minority issues. I myself was a minority, an Asian in white America, in schools and later in Wall Street where I worked."

As an undergraduate studying business and management at Columbia University in New York, he got involved in HIV work and hospice care with several volunteer organisations, including Gay Men's Health Crisis, the US' first group dedicated to the prevention of Aids.

He saw his fair share of horrifying deaths from the disease.

"During that time, people who had HIV were certain to die. You must remember anti-retroviral therapy was not really available until 1996 or 1997," he says, referring to the use of multiple drugs to effectively combat HIV.

At Columbia, he also interned at Wall Street firms and discovered he had a flair for trading and risk analysis.

In 1989, he enrolled in Harvard to get his master's in East Asian Studies, where he learnt modern Chinese history. His first job upon graduation was with Lehman Brothers, the fourth largest investment bank in the US before it declared bankruptcy in 2008.

The hours were punishing but he excelled at what he did - helping corporations with their initial public offerings and doing mergers and acquisitions - and was handsomely rewarded for it. His pay not only allowed him to buy an apartment but also to indulge in his love for opera as well as collecting snuff boxes.

His next stop was with Swiss bank UBS, which posted him to Hong Kong in 1995.

"I actually had no plans to move back to Hong Kong. But I guess fate played a hand and moved me closer to what I was meant to do," he says.

HIV was still an issue close to his heart. When the bachelor discovered that there was widespread ignorance about the disease in the former British colony, he got involved in outreach and prevention work.

The situation was even more dire in China, where his work often took him.

"I'd often ask the local people if they'd heard of Aids; a lot said no."

That led him to start CHF in 1998. Focused primarily on education and prevention, Mr To and volunteers would work with parties such as brothel owners to distribute condoms and promote safe sex among high-risk groups such as homosexuals and prostitutes. It also set up hotlines and websites to provide information and counselling services.

Three years after he set up CHF, he met a father and son in Beijing. They were from a remote village and were in the capital to seek medical treatment for HIV.

"Out of curiosity, I asked them how they contracted HIV. They said, 'Because we sold blood. Many people in our village sold blood too.' "

The duo were among thousands of victims of the "plasma economy", rampant in China in the 1990s.

Fuelled by demand from biotech companies, it attracted millions of people, mostly poor farmers and villagers, to sell blood for money.

Because of unsanitary practices and poor safety standards pertaining to the use of needles and blood bags, there was a surge in HIV infections that led to the disease gaining a firm foothold in the country.

In 2004, the Shanghai Daily newspaper cited a government report that put the number of registered HIV carriers in the country at 60,000 as of 2003. Experts, however, believed the number was closer to a million.

After meeting the father and son, Mr To visited a village in Henan where the number of infections was especially dire. He was stunned by what he saw. "In every household I visited, there were people who were either dying or had died of Aids," he says grimly.

Some scenes are still vivid in his memory.

"There was a man who had been dead in his home for two days. But none of his relatives and neighbours dared to go into his home to wrap his body. The lack of medical treatment was one thing; the lack of dignity struck me more," he says.

After he visited several villages, he realised he was too late to help the adults. "Many had died or were beyond help."

The children, however, could still be saved.

"Most of the children of those who died did not have HIV. But they stayed home, dropped out of school and had psychological problems because they saw their parents die. I realised that there would be a bigger social impact if we focused on helping the children."

He added: "If we did not help them, they would grow up with a lot of hatred; they'd be uneducated and it'd be very hard for them to find jobs."

It became clear to him that with the right help, these children could become social assets instead of potential liabilities.

Education is, Mr To explains, especially close to his heart.

"My great grandfather was a great believer in education. He said fortunes could be lost because of war, disaster and other circumstances, but with an education, you would always have something," he says, adding that the fortunes of his family over different generations have borne this out.

Not one to do things by halves, he gave up his job to steer CHF in a new direction. Friends thought he was crazy but he believed he knew what he was doing.

"I didn't have money to hire people, and people generally are still afraid of Aids, so I thought I'd do it myself," says Mr To, who tapped a network of friends, relatives and clients for funds when he first started out.

The strategic and management skills he picked up during his time in investment banking stood him in good stead.

He ruled out building orphanages or special schools, opting instead to work with the local school system to place these children.

"It's a more integrated approach. This way, the kids will also not be isolated from the community," says Mr To, whose foundation pays for school fees and other education-related expenses.

Besides scholarships, he has also started counselling services and psycho-social initiatives to help these children come to terms with their traumatic past.

The road was rocky in the beginning. Some were reluctant to accept his help for fear of being labelled. The authorities also watched him like a hawk, even raiding his office and seizing the computers of his Henan office.

But he kept at it.

Today, CHF has 12 offices throughout China and one in Hong Kong. It has helped 20,000 children in 260 villages in 14 provinces.

Over the years, major agencies, including the Global Fund, the Clinton Foundation and Hong Kong's Home Affairs Bureau, have come on board to support its initiatives. So have corporations like Cartier and fashion label MCM in Hong Kong.

The accolades he has won are many: 10 Most Inspiring Persons, 2004 (Hong Kong Government Department of Health), 50 Most Charismatic Persons in China, 2006 (People's Weekly Magazine), 10 Outstanding Young Persons of the World, 2006 (Junior Chamber International) and the 2007 Ramon Magsaysay Award for Emergent Leadership. The last was given for his "proactive and compassionate response to Aids in China and to the needs of its most vulnerable victims".

CHF now has 73 full-time staff.

"What makes me really happy is that 70 per cent of them are the Aids orphans we have helped. For me, that's a real success story. It means we have given them more than just an education. We have so empowered them that they have embraced their past."

Although advances in medication now mean HIV is no longer a death sentence, Mr To says his work is far from done.

"HIV is a social, not a medical, issue. There is still a lot of discrimination," he says. "As a service provider, as an NGO doing advocacy, we feel that society still needs a lot of education."

He is still in the front lines, interacting with families and children.

"I need to understand their changing needs. Only when I do can I get more effective programmes to help them."

Asked if he ever thinks about the banking life he left behind, he laughs.

"I'm happier," he says simply.