Former US President Barack Obama has proved the most popular of speakers that the Nelson Mandela Foundation has invited to deliver the Mandela lecture, with 15 000 people expected to attend the 16th edition at the Wanderers stadium in Johannesburg.

Former President Nelson Mandela and Obama, became the first black presidents of their respective countries yet met only once, in 2005 in a hotel room in Washington, while Obama was the senator from Illinois.

They spoke often by telephone while Obama was president.

At Madiba’s funeral in 2013 Obama described Mandela as one of modern history’s greatest liberators.

Obama said, “A boy raised herding cattle and tutored by the elders of his tribe. Madiba would emerge as the last great liberator of the 20th century like Ghandi he would lead a resistance movement. A movement, that had little prospect of success. Like Dr King he would give voice to the claims of the oppressed and a moral necessity of racial justice.”

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