Last Updated 12:26 p.m. ET
WASHINGTON - "An earthquake and hurricane may have delayed this day," said President Obama at the dedication of a memorial to Dr. Martin Luther King Jr., "but it was a day not to be denied."
Mr. Obama said Dr. King has returned to the National Mall - a symbol of the change he galvanized - at a ceremony attended by thousands.
The president said that King "stirred our conscience" and made the Union "more perfect."
Crowds began at dawn to crowd onto the memorial site, just to the southeast of the steps where King delivered his historic "I Have a Dream" speech. Designed as what King described as a stone of hope hewn from a mountain of despair, the memorial is the first to a black man on the National Mall and its parks, and the first monument to a non-president on the Mall.
"In this place he will stand for all time among monuments of those who fathered this nation and those who defended it," President Obama said, "a black preacher, no official rank or title, who somehow gave voice to our deepest dreams and our most lasting ideas - a man who stirred our conscience and thereby helped make our union more perfect."
"Some giants of the civil rights movement like Rosa Parks and Dorothy Height, Benjamin Hooks, Reverend Fred Shuttlesworth, they've been taken from us these past few years. This monument attests to their strength and their courage. And while we miss them dearly, we know they rest in a better place.
"Finally, there are the multitudes of men and women whose names never appear in the history books. Those who marched and those who sang, those who sat in and those who stood firm. Those who organized and those who mobilized - all those men and women who through countless acts of quiet heroism helped bring about changes few thought were even possible ... faceless, anonymous, relentless young people, black and white, [who] have taken our whole nation back to those great wells of democracy which were dug deep by the founding fathers in the formulation of the Constitution and the Declaration of Independence. To those men and women, those foot soldiers for justice, know that this monument is yours as well."
Mr. Obama (who was 6 when King was assassinated) credits him with helping to pave his way to the White House as the nation's first black president.
Aretha Franklin, Stevie Wonder and poet Nikki Giovanni were among those who honored the legacy of the nation's foremost civil rights leader.
Today's ceremony had been postponed from its original scheduled dat4e by Hurricane Irene.
Some attendees started lining up at 5 a.m. and even earlier Sunday morning. Organizers anticipate as many as 50,000 people will attend. By 9 a.m., thousands of seats were filled, and attendees were greeted with bright sunlight.