Anti-apartheid icon Nelson Mandela turns 88 on Tuesday and despite being in exceptional health for his age, South Africa's favourite son is appearing less and less in the public eye.

Madiba, as Mandela is affectionately known by his Xhosa clan name, will spend a quiet birthday with his family at his home in Qunu, in South Africa's rural Eastern Cape province, his foundation said.

"Madiba will have no public engagements at all on Tuesday," the Nelson Mandela Foundation's Verne Harris said this week, saying the shift from his public larger-than-life persona to a more private one, came at the Nobel peace laureate's own request.

"This shift is taking place in response to Madiba's own request. He has retired formally from public life," Harris said, referring to an announcement made two years ago.

But although Mandela on a personal level has withdrawn largely from public engagements, his foundation is continuing to capture the legacy of one of the world's best-known figures.

"Madiba has given us at the foundation his personal mandate to shift to memory and dialogue work," said Harris.

The shift to capture Mandela's legacy through remembrance -- including photo exhibitions of his early years and a tribute to his former university -- is seen as an acknowledgment that the statesman who steered South Africa after its first democratic elections in 1994, will not be around forever.

Although his health is slowly failing, Mandela remains in remarkably good shape for a man his age and somebody who spent almost three decades of his life in prison.

"His short term memory is not up to scratch, according to those close to him, and his knees are causing him distress," the Saturday Star reported over the weekend.

"But he remains in good spirits and his 'almost wicked' sense of humour... shows no sign of disappearing," the paper said.

The elderly statesman last week demonstrated his sense of humour when he joked with long-time friend and veteran photographer Alf Khumalo, who is staging a photo exhibition of Mandela's early days as a lawyer.

Ah Alf, I see you're still here. You should go on retirement," a broadly beaming Mandela told his friend, referring to his own withdrawal from public life which he often refers to as "retirement from retirement".

Yet, despite the "public" Mandela becoming a "private" one, he still has a punishing schedule of engagements to fulfil around his birthday.

It started last week with the launch of a book of a series of lectures by prominent black thinkers on the 'Meaning of Mandela' -- and the photo exhibition by Khumalo and another veteran, Jurgen Schadeburg.

His next appearance is scheduled for Thursday, where he and other graduates of Fort Hare University will be given honorarium rings.

A week later, on July 29, his birthday will be capped by a speech given by President Thabo Mbeki in his honour at the Nelson Mandela Annual Lecture.

While Mandela celebrates another birthday next week in public and in private, his legions of well-wishers will no doubt reflect on just what his legacy means.

"Madiba means so many things to so many people," said academic Xolela Mangcu, who compiled the 'Meaning of Mandela' with lectures by American thinkers Henry Louis Gates Jr, Cornel West and Nigerian writer Wole Soyinka.

"But the only thing that brings people together is the idea of freedom, the idea of plurality and the idea of tolerating each other."

"That's what Nelson Mandela stands for," he said. - AFP