Obama embodies King's 1963 dream
President Barack Obama led civil rights pioneers in a ceremony for the 50th anniversary of the March on Washington, where Dr Martin Luther King's "I Have a Dream" speech roused the 250,000 people who rallied there for racial equality.
Large crowds gathered at the Lincoln Memorial, where the first black US president spoke just after 7pm GMT - the same time that Dr King delivered his spellbinding speech.
The first march was early in the turbulent 1960s, when the South still had separate toilets, schools and careers for blacks and whites and racism lingered across the country. In the two years following the march, President Lyndon Johnson signed the landmark Civil Rights Act and Voting Rights Act to outlaw discrimination and Dr King received the Nobel Peace Prize.
"There were couples in love who couldn't marry. Soldiers who fought for freedom abroad but couldn't find any at home," Mr Obama said, speaking of that era. "America changed for you and for me," he added later. But he pointed to the nation's economic disparities as evidence that Dr King's hopes remain unfulfilled. "The arc of the moral universe may bend toward justice but it doesn't bend on its own," Mr Obama said, in an allusion to Dr King's own message.
The name of that original march was the March on Washington for Jobs and Freedom.
Mr Obama has said Dr King is one of two people he admires "more than anybody in American history". The other is Abraham Lincoln. Thousands of people gathered on Wednesday in wet weather. Two former presidents, Bill Clinton and Jimmy Carter, spoke movingly of Dr King's legacy - and of problems still to overcome. "This march, and that speech, changed America," Mr Clinton declared. Mr Carter said Dr King's efforts had helped not just black Americans, but "in truth, he helped to free all people".
Oprah Winfrey and actors Forest Whitaker and Jamie Foxx were among the celebrities. Winfrey said Dr King forced the nation "to wake up, look at itself and eventually change".
International commemorations were held in London's Trafalgar Square, as well as in Japan, Switzerland, Nepal and Liberia. London mayor Boris Johnson has said Dr King's speech resonates around the world and continues to inspire people as one of the great pieces of oratory.
On August 28 1963, as Dr King was ending his speech, he quoted from the patriotic song My Country 'Tis Of Thee and urged his audience to "let freedom ring". "When we allow freedom to ring - when we let it ring from every city and every hamlet, from every state and every city, we will be able to speed up that day when all of God's children, black men and white men, Jews and Gentiles, Protestants and Catholics, will be able to join hands and sing in the words of the old Negro spiritual, 'Free at last, free at last, great God almighty, we are free at last'," Dr King said.
The civil rights leader was assassinated five years later.