Yolanda Denise King, the oldest child of civil rights leader the Rev. Martin Luther King Jr. died late Tuesday in Santa Monica, California at age 51.  Relatives think it might have been a heart problem.

King was an actor, speaker, producer and the founder and head of Higher Ground Productions, billed as a "gateway for inner peace, unity and global transformation." On her company’s Web site, King described her mission as encouraging personal growth and positive social change.

She was also an author and advocate for peace and nonviolence, and held memberships in the Southern Christian Leadership Conference — which her father co-founded in 1957 — and the National Association for the Advancement of Colored People.

Her death comes more than a year after the death of her mother, Coretta Scott King.

In 2005, King presented the Gavin Newsom Visionary Award at the Fourth Annual Equality Awards & Gala to the California State Conference of the National Association for the Advancement of Colored People (NAACP) for their support of marriage for gays and lesbians. King was known for her support of lesbian and gay  civil rights and was a popular speaker at LGBT events.

She was among 187 protestors in 2000 that went to jail to make an impression on the United Methodists and the Archbishop of Canterbury in Cleveland, Ohio in a civil disobedience action seeking equal treatment from religious groups for lesbian, gay, bisexual, and transgendered people.