He quit his job, set up a charity and has devoted himself to its work and the children ever since.

“My decision at that time was seen by everybody as weird,” he said.

“People said, ‘if you sympathise with them, you can donate money and go back to your job’. But the ordeal of those kids had touched my heart and I felt an urgent need to provide more help for them.”

Since 2002, his Hong Kong-registered Chi Heng Foundation has sponsored more than 23,000 Chinese Aids orphans to go to school, of whom 5,000 have entered university or college, at a cost of more than 200 million yuan (US$29 million).

Additionally, To has tried to build the children’s self-esteem and broaden their horizons by taking them to summer camps and on visits to top universities and big enterprises in mainland metropolises.

“I get along closely with these kids. We regard each other as family,” said To, who is often dubbed a “dad” to tens of thousands of Aids orphans.

Many of the children come from Henan, which was plagued by HIV/Aids in the 1990s after farmers were encouraged by local authorities to sell blood to relieve their poverty.

But unhygienic syringes led to a massive regional outbreak of HIV, the virus that causes Aids, and many deaths in the years to come.

Compared with 20 years ago – when HIV was a taboo topic in mainland China – the current attitude of the authorities has more or less completely turned around.

A national Aids prevention and treatment programme has been in effect for more than 10 years and Aids patients are entitled to free medication for life.

Peng Liyuan, wife of Chinese President Xi Jinping, advocates for education and treatment at home and abroad as both a national and World Health Organisation ambassador for HIV prevention.

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Even so, To said, there is still discrimination towards people affected by the disease and that is an area where he would like to see improvement.

“Both the government and domestic media don’t think HIV is a sensitive issue now and there are no problems in that regard,” he said.

“However, I don’t see progress in the public perception of Aids patients and other people affected by the disease.

“Patients with HIV have trouble going to school, finding a job and receiving medical treatment,” he said.

In one case, To said, an orphan sponsored by his foundation was admitted to a mainland Chinese university – but was soon urged to quit when the school found out he was HIV-positive.

“This student wouldn’t agree to quit the school and was told to live in a rented room outside the campus, rather than in the dormitory with his peers,” To said. “It’s so unfair.”

In some cities, Aids patients are banned from using public bathing pools, because venue owners think people can contract the virus through sharing the facilities.

“I normally deliver 40 to 50 speeches a year at universities across the country, hoping to alleviate people’s ignorance and the prejudice that [leads them to think] people with HIV should be isolated,” To said.

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To was born in Hong Kong in 1967 and moved to San Francisco, California, at the age of 14. He earned a bachelor’s degree from Columbia University in New York and a master’s from Harvard University’s Asia Centre.

After graduating from Harvard, To joined Lehman Brothers and later UBS, which sent him to work as a vice-president in its Hong Kong office in the 1990s.

While working at UBS, he travelled a great deal across China on business and was shocked to find that people on the mainland did not know what Aids was.

To had been aware of HIV/Aids since growing up in the 1980s in San Francisco, the global centre of the Aids epidemic and one of the cities worst hit by HIV at that time.

“There were no drugs for the patients,” he said. “One of my high school teachers died from this disease.”

In 1998, To registered Chi Heng Foundation with a mission to foster HIV prevention and education. For four years his charitable work was a part-time endeavour. That changed when he visited Henan.

To had heard that many people in the province had contracted HIV while selling blood, so he went to see the situation for himself.

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A visit to a rural family in 2001 was the “defining moment” in his life, he said, and prompted him to devote himself full-time to the HIV charity the following year.

The family had already lost their father who had died from Aids. The youngest child, a boy, was seriously ill with the disease which he had probably contracted from his mother. His older sister was the only member of the family who was healthy.

Their mother asked To to save her son. “I will never forget the eyes of that boy,” he said. “He desperately wanted to live.”

Before that moment, To’s life was comfortable and he was unaware of how different circumstances could be for others who were less fortunate.

“I thought the world was like that. I did not see people’s ordeals,” he said.

“When you see a situation like that, I believe few people would not be moved and would not want to do something for them.”

To told the mother that all he could do was help to sponsor her daughter’s education. Several days later, the boy died.

After that trip, To said he saw many more families suffering from similar miseries caused by HIV/Aids and became increasingly aware of his good fortune.

He said he realised he could go to the US, study at the best universities and have a good job, not because he was smart or worked diligently, but because he was lucky.

“Those poor farmers in Henan were also smart and also worked diligently,” To said.

“But they were unlucky, so they had to sell blood and be infected by HIV. Therefore, I have a humble heart to help those unfortunate people.”

In 2002, he quit his UBS job and his foundation started financing the education of Chinese children with at least one parent who had contracted HIV or died from Aids.

“Although the number of Aids orphans we have helped account for a small number of the whole [affected] group in China, I feel no guilt because I have tried my best to help as many as I can,” he said.

To said that in the first few years of his work in China, he often woke in the night to find he had been crying in his dreams after seeing the difficult lives of the Aids orphans during the day. He was on the brink of depression.

There was added stress in those years because he was often monitored or even followed by the authorities who were trying to cover up the epidemic.

In 2003, following pressure from the international community, China admitted the situation and Premier Wen Jiabao visited Aids patients in hospitals and shook their hands. Since then To’s charity has successfully registered in China and developed a better relationship with the mainland authorities.

He has received praise and honours from China and other countries, including, in 2007, the Ramon Magsaysay Award, issued annually by the Philippines, and known as Asia’s Nobel Peace Prize.

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During the past two decades, To said, he has been offered chances to return to his previous life in banking, but he has declined because, he said, he thinks “chasing happiness is more important than chasing money”.

“I feel most happy when seeing that the kids we sponsored have grown up, gone to university or are getting married,” To said.

Among the 23,000 orphans his charity has helped, fewer than 10 per cent are carriers of HIV. For the past four years or so, To’s organisation has also been doing some matchmaking for HIV-positive individuals.

“It’s hard for people with HIV to make friends in the society, not to mention to find a partner,” he explained.

So far 68 couples, with both partners HIV positive, have tied the knot and 72 babies have been born.

Thanks to advances in medical technology that prevent mother-to-baby transmission of the virus, every single one of those children is free of the disease.

“This delightful result is a powerful hit to the stigma against Aids patients,” To said.