In 2004, at the age of 85, Mr Mandela retired from public life to spend more time with his family and friends and engage in "quiet reflection".
On Friday, he appeared before reporters to say: "There are many people in South Africa who are rich and who can share those riches with those not so fortunate who have not been able to conquer poverty".
The fight against poverty is one of the causes taken up by Mr Mandela, the BBC's Peter Biles reports from Johannesburg.
Three years ago, the former president attended a huge rally in London as part of the Make Poverty History campaign.
Mr de Klerk, who was awarded the 1993 Nobel Peace Prize along with Mr Mandela, said the former president was a born leader with the "assurance, the humility and the grace of a true natural aristocrat".
1918 - Born in the Eastern Cape
1964 - Sentenced to life for high treason
1990 - Freed from prison
1993 - Wins Nobel Peace Prize
1994 - Elected first black president
2004 - Retires from public life
2005 - Announces his son has died of an HIV/Aids-related illness
As president, he added, Mr Mandela had "used his personal charm to... mould our widely diverse communities into an emerging multicultural nation".
Friday also marks 10 years since Mr Mandela married his third wife, Graca Machel.
"He is simply a wonderful husband... and we enjoy every single day as if it is the last day," she told CNN.
The official birthday party is due to be held on Saturday in a gigantic white marquee erected in Qunu village.
Three cows are to be slaughtered for the festivities, with the banquet menu featuring traditional food such as tripe and sheep's heads, AFP news agency reports.
Birthday celebrations abroad have been going on for several weeks, including a concert in June in London's Hyde Park.
In other birthday events, reported by the South African Press Association:
The Eastern Cape agricultural department gives at least 150 goats to poor communities
The ANC unfurls two huge banners of Mr Mandela on the side of its headquarters, Luthuli House
Many of those who have worked with Nelson Mandela and had a close friendship with him over the years say that behind the adulation he inspires there is a very human and often extremely private figure, the BBC's Mike Wooldridge reports.
Three generations reflect on Mandela
Fellow Robben Island prisoner Mac Maharaj told our correspondent Mr Mandela was truly an icon.
He reduced a veteran white police officer to tears on his inauguration day when he walked over to him, shook his hand and told him "today you have become our police".
But Mr Maharaj argues that the event that sheds most light on Nelson Mandela's character was the killing of the popular ANC leader Chris Hani in 1993.
Mr Maharaj believes that if Nelson Mandela had called for an insurrection in response it would have been unstoppable but, instead, he went on television to call for calm and commitment to democracy.
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