Again, none of them cozied up to murderous dictators.

JOHANNESBURG — Celebrating one of his personal heroes, President Barack Obama praised Nelson Mandela as the last great liberator of the 20th century, urging the world to carry on his legacy by fighting inequality, poverty and discrimination.

At a memorial service in Johannesburg, Obama compared the former South African President to Mahatma Gandhi, Martin Luther King Jr. and Abraham Lincoln. He said Mandela had earned his place in history through struggle, shrewdness, persistence and faith.

“For nothing he achieved was inevitable,” Obama said. “In the arc of his life, we see a man who earned his place in history through struggle and shrewdness, persistence and faith. He tells us what’s possible not just in the pages of dusty history books, but in our own lives as well.”