President Obama summoned young Africans, who make up 60 percent of the continent’s population, to fight corruption and bolster the democratic advances on the continent in order to fulfill the legacy of South Africa’s beloved former leader Nelson Mandela.

“Nelson Mandela showed us that one man’s courage can move the world,” Obama said during an evening speech at the University of Cape Town, standing in front of a backdrop of smiling college students of multiple nationalities and races.

His remarks were billed as the signature speech of Obama’s week-long tour of the sub-Sahara and came after an emotional day that included a visit to Robben Island where Mandela spent 18 out of 27 years locked up under the rule of the minority white-controlled government.

The life of the ailing 94-year-old anti-apartheid hero is hanging in the balance as he fights a lung disease and is in critical condition in a hospital.

In deeply personal remarks, Obama recalled his morning visit to Mandela’s cramped Robben Island cell with his two daughters, Malia and Sasha.

“Seeing them stand within the walls that once surrounded Nelson Mandela, I knew this was an experience they would never forget,” he said. “I knew they now appreciated a little bit more [the sacrifices] Madiba and others had made for freedom,” he said, referring to Mandela by his clan name.

Obama also repeatedly talked about the United States’ own rocky civil rights path, noting that 50 years ago Robert F. Kennedy delivered his famous “Ripple of Hope” speech at the same university, which inspired his own remarks.

Kennedy’s speech (an audio excerpt of which is embedded in the video player below this post), was delivered after Mandela was sentenced to prison and called on young people to launch a world-wide fight against racial segregation and injustice, creating ripples of hope that would “build a current, which can sweep down the mightiest of walls of oppression and resistance.”

Mandela’s courage against the brutality leveraged against him and Kennedy’s speech, Obama said, inspired him to attach himself to a political movement for the first time in his life, back when he was in college.

“I knew that brave people were imprisoned — and that my own government in the United States was not standing by their side, and that’s why I got involved in what was known as the divestment movement in the United States,” he said.

During the speech, Obama also called on America to “up its game when it comes to Africa” in promoting trade and investment in some of the fastest growing economies in the world.

He unveiled a new plan to double access to electric power in the sub-Sahara with an initial $7 billion commitment from the U.S. during a speech at the University of Cape Town later Sunday.

“Access to electricity is fundamental to opportunity in this age…”ya gotta have power,” he said.

Private power companies General Electric and Symbion Power are providing an additional $9 billion to the project.

While other countries like China are investing in Africa at a rapid rate, he said the U.S. commitments carry with them democratic ideals to help African countries fight corruption, oppression and terrorism.

While some in Africa will accuse the U.S. of “meddling,” by urging democratic reforms, he said history is on America’s side because “true progress happens where governments exist to serve their people and not the other way around.” The crowd erupted in thunderous applause.

Earlier that day, Obama and the first family were led on a tour of Robben Island Sunday by 83-year-old Ahmed Kathrada, who was imprisoned there with Mandela for nearly two decades during the anti-apartheid movement. He is the same guide who took Obama on a 2006 visit to the prison while a senator, although Obama made that tour alone without his family.

With Michele, Sasha and Malia in tow, Kathrada led Obama into the prison courtyard where Mandela, during his imprisonment planted grapevines that remain today, and where he an fellow prisoners would swap notes and hide writings.

After visiting the Mandela’s narrow cell, Obama and Michelle signed a guest book in the courtyard.

“On behalf of our family, we’re deeply humbled to stand where men of such courage faced down injustice and refused to yield,” he wrote. “The world is grateful for the heroes of Robben Island, who remind us that no shackles or cells can match the strength of the human spirit.”

The tour included a stop at the lime quarry where Mandela and fellow prisoners was forced to spend their time breaking rocks, the place where Mandela developed the lung problems that are threatening his life today.

Afterward, Obama visited a community center run by Archbishop Desmond Tutu that offers after school support – English conversation and computer learning – for young children. The archbishop, wearing a pink cassock and a large silver cross, took Obama on a tour of the facility.

While Obama visited with six young boys in one classroom, one student held the president’s children’s book, “Of Thee I Sing,” which Obama acknowledged and signed.

This story was based in part on wire reports.