Most of us knew him only from the iconic image we saw on television: a tiny, wizened man-child clutching a microphone that seemed almost as big as he was, speaking with a voice that was biblical in its resonance. Suffer the little children, he seemed to say. But please do not let them suffer as much as me.

Nkosi Johnson died peacefully in his sleep yesterday morning, weighing just 22lbs. He was only 12 years old. ''His race was run and I think we knew that a long time ago. I'm exceptionally proud of him,'' his adoptive mother said.

This tiny, adorable South African boy with Aids had an impact that spread across the world, influencing politicians and moving millions to tears. Singlehandedly, Nkosi challenged humanity to face up to their prejudice against the disease that was laying waste to a quarter of his country.

He was born HIV-positive and abandoned by his mother because she feared her neighbours' prejudice when they discovered his condition. As a toddler, Nkosi was sent to a hospice to die, one of the 200 HIV babies born every day in South Africa. Few live to see their second birthday, and it is estimated that seven million South Africans will fall victim to the disease within the next decade. Both Nkosi's parents died from Aids.

Proximity to death turns children old far beyond their years, and Nkosi was no exception. In his brief, saintly life he displayed extraordinary maturity and dignity, becoming, as Nelson Mandela put it, an icon for the struggle for life itself.

Last July, at the International Aids Conference in Durban, a composed Nkosi took to the stage in front of thousands of delegates. The impression of an old soul in a child's body was heightened by the suit and tie that hung, several sizes too big, upon his pitifully wasted body.

He held scientists, ministers, and activists spellbound, reducing many to tears, as he said: ''I want people to understand Aids - to be careful and respect Aids. You can't get Aids if you touch, hug, kiss, hold hands with someone who is infected. Care for us and accept us, we are all human beings, we are normal. We have hands, we have feet, we can walk, we can talk, and we have needs just like everyone else, don't be afraid of us.''

For all his tiny voice in his small body, Nkosi was blessed with huge charisma: the power, perhaps, that those close to death retain over the living. ''I never even knew I had a father,'' he told the conference. ''Infected mummies and daddies shouldn't be separated from their children. I know my mother is in heaven and she is in my heart and is watching over me. I think I will see her there and maybe we will dance together. My foster mother has told me heaven is a very happy place.''

Nkosi then attacked the South African government's failure to supply the anti-Aids drugs. He said: ''I just wish that the government can start giving AZT to pregnant HIV mothers to help stop the virus being passed on to their babies. Babies are dying very quickly and I know one little abandoned baby who came to stay with us and his name was Micky. He couldn't breathe, he couldn't eat, and he was so sick and my mummy Gail had to phone welfare to have him admitted to a hospital and he died. But he was such a cute little baby and I think the government must start doing it because I don't want babies to die.''

In an electric moment, Thabo Mbeki, the South African president, who controversially had questioned the sexual link between HIV and Aids and the safety of Aids drugs, walked out of the conference in the middle of the speech. Aides said later he was pressed for time.

The threat Nkosi posed to the politicians was highlighted by the subsequent whispering campaign against his foster mother, accusing her of exploitation. Only yesterday, after his death, was Gail Johnson cleared of an allegation that she had abused Nkosi by giving the impression he was sicker than he was in order to raise money for herself.

What made the allegations more distressing was that since last December Nkosi has been semi-conscious with Aids-induced brain damage and viral infections. In the last few months, hanging on through sheer strength of spirit, he was unable to eat and was fed by a tube.

Highly symbolic political gestures were made, however. On his deathbed Nkosi was visited by Mbeki's wife Zanele. The boy said he wanted to meet Mbeki himself; the president never came.

Up until the very end, Nkosi was still capable of squeezing Gail Johnson's hand and smiling. Poignant as it was, he had reason to smile. The South African government recently changed its stance and promised that pregnant women will get AZT. They threatened to take drug companies to the Supreme Court to force them to lower their prices for anti-Aids drugs, resulting in a rapid capitulation by the cartel.

There have always been almost messianic echoes in Nkosi's story: of abandonment, rejection, and sanctification through suffering. After being left as a baby, he was put in a hospice - the only black among rooms of white, homosexual South African men - which had been founded by Gail Johnson. When the hospice was forced to close through lack of funds, Ms Johnson took Nkosi home and nursed him, enabling him to survive longer than any other child in the country.

He came to national prominence when he was turned away from a predominantly white school in the Johannesburg suburb of Mellville because it was feared he would infect other pupils. Ms Johnson, a feisty white woman famous for her thick make-up and her ability to use the media, took up her son's cause and after a high-profile battle he was accepted and became, through his extraordinary natural charm, the most popular child in school. Shortly before his death, his headmaster said 80% of the pupils in his school did not know he had Aids.

His case led to a policy forbidding schools from discriminating against HIV-positive children and to guidelines for how schools should treat infected pupils. While still healthy enough, Nkosi helped raise money for Nkosi's Haven, a Johannesburg shelter for HIV-positive women and their children.

Nkosi had a warm sense of humour and would often try to get out of household chores such as feeding the family's five cats. Shortly before his collapse in December, he told Ms Johnson he was sorry for letting her down.

His death was greeted by almost religious fervour and to the last Ms Johnson was being accused of making the boy the centre of a media circus. Cars crammed the narrow street outside his home, healers arrived to offer advice, local celebrities came with flowers, politicians and Aids activists lined up at the gate with journalists.

''He was a very courageous young man, a courageous child. And I think he became a wonderful advocate and was able to reach many people beyond South Africa,'' UN secretary-general Kofi Annan said in Washington. ''We have lost a voice.''

Nelson Mandela said: ''It is a great pity that this young man has died. He was very bold.''

All mourned a child with a vast spirit whose voice was both utterly frail, yet powerful enough for the whole world to hear it.