Yolanda King, the Rev. Martin Luther King Jr.'s eldest child who pursued her father's dream of racial harmony through drama and motivational speaking, collapsed and died after making a speech. She was 51.

King died late Tuesday in Santa Monica, Calif., said Steve Klein, a spokesman for the King Center. The family did not know the cause of death, but relatives think it might have been a heart problem, he said.

"She was an actress, author, producer, advocate for peace and nonviolence, who was known and loved for her motivational and inspirational contributions to society," the King family said in a statement.