"She lived with a lot of the trauma of our struggle," said the Rev. Jesse Jackson, who worked with her father. "The movement was in her DNA."
The Rev. Al Sharpton called King a "torchbearer for her parents and a committed activist in her own right."
White House press secretary Tony Snow said President Bush and the first lady were sad to learn of King's death, adding, "Our thoughts are with the King family."
"This is just the last thing and the last person that we expected this to happen to," said Issac Newton Farris, the Kings' cousin and CEO of the King Center in Atlanta. "At least with my aunt (Coretta Scott King) we had some warning. Yolanda as far as we knew was healthy and certainly happy."
Former Mayor Andrew Young, a lieutenant of her father's who has remained close to the family, said King died Tuesday after collapsing in a Santa Monica doorway while on her way to her brother Dexter's home. Farris said she died near Dexter King but would not elaborate.
Family members did not know the cause of death, but suspect it might have been a heart problem.
The oldest of the four children of civil rights trailblazers Rev. Martin Luther King Jr. and Coretta Scott King, Yolanda lived in California and appeared in numerous films, including "Ghosts of Mississippi," and played Rosa Parks in the 1978 miniseries "King." She also ran a production company.
"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.
"She used her acting ability to dramatize the essence of the movement," said Rep. John Lewis, D-Ga., who worked alongside King's father. "She could motivate and inspire and tell the story. I heard her recite 'I Have A Dream' on several occasions. She made it real, made it part of her. I think her father would've been very, very proud of her."
Yolanda King's death came less than a year and a half after Coretta Scott King died in January 2006 after battling ovarian cancer and the effects of a stroke. Her struggle prompted her daughter to become a spokeswoman for the American Heart Association, raising awareness, especially among blacks, about stroke. A spokeswoman for the group said she last spoke on the organization's behalf on Saturday at a hospital in Langhorne, Pa.
She was just two weeks old when Rosa Parks refused to give up her seat on a bus there, leading to the Montgomery bus boycott spearheaded by her father. When the family's house was firebombed eight weeks later, she and her mother were at home but were not hurt.
She was a young girl during her father's famous stay in the Birmingham, Ala., jail. She was 12 years old when he was assassinated in Memphis, Tenn., in 1968.
Yolanda King founded and led Higher Ground Productions, billed as a "gateway for inner peace, unity and global transformation." On her company's Web site, she described her mission as encouraging personal growth and positive social change.
Yolanda, said Andrew Young, "didn't want to be a child of the movement, she wanted to be what God wanted her to be... She could never escape being a child of the movement, though. She was really feeling that she didn't just want to be the daughter of Coretta and Martin King. That was her struggle."
The flag at The King Center, where she was a board member, flew at half-staff on Wednesday.
In 1963, when she was 7, her father mentioned her and her siblings at the March on Washington, saying: "I have a dream that my four little children will one day live in a nation where they will not be judged by the color of their skin but by the content of their character."
Her brother Martin III was born in 1957; brother Dexter in 1961; and sister Bernice in 1963. Each of the siblings, in their own way, have worked to carry on their parents' work.
King was a 1976 graduate of Smith College in Northampton, Mass., where she majored in theater and Afro-American studies, an area of study which at that time was just beginning to be offered at only a handful of colleges. She also earned a master's degree in theater from New York University.
Yolanda King was the most visible of the four children during this year's Martin Luther King Day in January, the first since her mother's death.
Using her craft as an actress to deliver a tribute to her parents, Yolanda performed a series of skits telling stories including a girl's first ride on a desegregated bus and a college student's recollection of the 1963 desegregation of Birmingham, Alabama.
Asked at that ceremony how she was dealing with the loss of her mother, Yolanda responded: "I connected with her spirit so strongly. I am in direct contact with her spirit, and that has given me so much peace and so much strength."
Speaking then in Atlanta at Ebenezer Baptist Church - where her father preached for many years - Yolanda exhorted those observing the national holiday that bears his name to remember that America has not yet achieved peace and racial equality.
"We must keep reaching across the table and, in the tradition of Martin Luther King Jr. and Coretta Scott King, feed each other," said Yolanda, urging those who honor the Kings' work to question their own beliefs on prejudice and be a personal force for peace and love.