President Barack Obama saluted Dr. Martin Luther King Jr. Sunday as a man who "stirred our conscience" and made the Union "more perfect," rejoicing in the dedication of a monument memorializing the slain civil rights leader's life and work.

"I know we will overcome," Obama proclaimed, standing by an imposing granite monument on the National Mall. "I know this," the president said, "because of the man towering over us."

Obama and his wife, Michelle, and Vice President Joe Biden and his wife, Jill, joined a host of civil rights figures for the dedication on the sun-splashed Mall.

"He had faith in us," said Obama, who was 6 when King was assassinated in 1968. Obama told the crowd, "And that is why he belongs on this Mall: Because he saw what we might become."

Obama credits King with paving his way to the White House. Before his remarks, the president left a copy of his inaugural speech in a time capsule at the monument site.

Crowds began to gather at dawn at 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.