He wore a trendy black shirt just like many of the kids in the crowd. But Nelson Mandela moved slowly, leaning on his wife and on a white cane as he crossed the stage to adoring cheers.

Public appearances like the one at the London rock concert in honour of his birthday are rare these days for the anti-apartheid icon.

Mandela jokes he has "retired from retirement", but this time it sounds serious. The tall, majestic figure the world saw walking out of prison to freedom 18 years ago is now gray-haired, frail and for the most part silent as he reaches his 90th birthday on Friday.

When he turned 89 on July 18 2007, Mandela celebrated by announcing the founding of a "council of elders" -- fellow Nobel peace laureates, politicians and development gurus pooling their wisdom and influence to tackle global crises. Elders have since jetted to Darfur and the Middle East -- but Mandela has stayed at home.

As South Africa's first black president -- he only ran for one term -- Mandela ushered in a democratic, multiracial society that is still going peaceful and strong.

There are occasional bumps, some sharp. But overall, the Mandela era has confounded doomsayers at home and abroad who doubted South Africa's races could live together under black rule.

After changing his country so profoundly, then turning his energies during his first "retirement" to tackling problems like Aids, Mandela has left the stage to younger leaders. But South Africa and the world seem reluctant to let him fade into retirement.

When crises break out -- the collapse of neighbouring Zimbabwe, a crime wave at home, or violence against African immigrants over jobs and housing -- South Africans expect to hear from Mandela.

"I want this great leader to come back," said Stephen Miller, a composer. "It's extraordinary nostalgia."

Faith van den Heever epitomises the epic changes South Africa has undergone. She is a white woman who coaches young black players at rugby, a sport black people once universally associated with whites, and reveres a man who used to be reviled by the white leadership as a communist and a terrorist.

"I feel Madiba is one of the best things that could have happened to the country," she says, using the clan name by which South Africans affectionately refer to Mandela.

World affairs
Mandela has given no interview in years. Increasingly, he leaves the pronouncements on world affairs to officials of the foundation he established upon retiring. Last month, when he spoke up about Zimbabwe President Robert Mugabe's rampage against democratic change, he did it at a private dinner in London, and his remarks, conveyed by his aides, seemed relatively mild.

He called Zimbabwe's agony a "tragic failure of leadership" -- very different from the harsh language he used against the United States in 2003, when he accused it of committing "unspeakable atrocities in the world".

Mandela will spend his birthday privately with family in Qunu, his boyhood village 1 000km south of Johannesburg.

There, he built a replica of the house in which he was held briefly after being moved off Robben Island, the desolate offshore prison where he spent most of his 27 years.

Mandela wrote in his autobiography, Long Walk to Freedom, that he chose to recreate the home because he knew it well and "would not have to wander at night looking for the kitchen".

Mandela has been married three times. Winnie Madikizela-Mandela, his second wife, has been active in politics since their 1996 divorce. He spends much of the year in Maputo, the relaxed seaside capital of neighbouring Mozambique, homeland of this third wife, Graca Machel, in a home filled with her grandchildren and his.

However sheltered his life has become, Mandela remains a vivid presence for many South Africans, white and black. Despite 5% annual economic growth achieved under his successor, Thabo Mbeki, half the population still lives in poverty, unemployment is 25%, crime is rampant and, whenever things look especially bleak, the instinct seems to be that things would be different under Mandela.

Racial gap
The racial gap that Mandela sought to narrow by word and example is still glaring in the richer neighbourhoods, where white people own the homes and black employees do the gardening. Their children attend the same classes -- one of many post-apartheid reforms -- and white parents marvel at how well they get along. But they also see the vast gap between the white children's toy-filled homes and the one-room servants' quarters of their black schoolmates.

Still, most South Africans would agree that life is better than before Mandela came to power -- less volatile, fairer, less uncertain, more democratic. Only a few cranks try to justify apartheid in public.

In Mandela's remarks in London, he concluded with words to the young, saying: "It is now in the hands of your generations to help rid the world of such suffering."

He could have been referring to people like Ntobeko Peni, a black man who once believed all whites in South Africa were the enemy, but now says he learned from Mandela to value them as partners in nation-building.

In 1993, Peni, then 20, was among a mob of blacks in Cape Town who attacked Amy Biehl, a visiting white American democracy scholar. Peni and three other men were convicted of stabbing and stoning her to death in what became one of the most infamous episodes of the immediate post-apartheid era.

In 1998, Peni was granted amnesty after confessing before the Truth and Reconciliation Commission that Mandela's government established to help unite the country after apartheid. Biehl's parents publicly forgave him and he now works for the Amy Biehl Foundation, running mentoring programmes and music classes for black kids.

Peni, now 35, says Mandela became his role model by his words and deeds.

A turning point, he says, was watching on the prison TV as South Africa's rugby team won the 1995 World Cup and Mandela walked on to the field to congratulate the team. He saw Mandela wearing the team jersey, once the hated symbol of white exclusivity, and he saw the white captain, Francois Pienaar, present the trophy to his black president.

"When I saw that," Peni said, "I saw cooperation -- that we could work together." -- Sapa-AP