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From the moment that Dora McDonald became Rev. Martin Luther King Jr.’s personal secretary in 1960, she was entrusted with his secrets and counted on to look after his family if something happened to him.

It was Ms. McDonald who often got late-night calls from King when he couldn’t sleep. It was Ms. McDonald who typed King’s manuscripts and the final versions of his speeches. She was the one who told Coretta Scott King that her husband had been assassinated.

Ms. McDonald, who was born in Greeleyville, S.C., died of complications from cancer at Crawford Long Hospital on Saturday, two days before the national holiday that honors her former boss and friend. She was 81.

“She was more than Martin’s secretary,” said civil rights leader Joseph Lowery. “She was his confidant, his colleague. She loved him, and he loved her. We all loved Dora.”

Saturday night at the Salute to Greatness awards ceremony, held annually in Atlanta in King’s honor, attendees observed a moment of silence to mark Ms. McDonald’s death.

As King’s secretary, Ms. McDonald tended to his everyday affairs, such as his finances, correspondence and travel arrangements, from her desk at Ebenezer Baptist Church and later from her office at the Southern Christian Leadership Conference.

“It was a 24-hour-a-day, seven-day-a-week job,” she told The Atlanta Journal-Constitution in 1989. “But there was never a time–and I can say this in all truthfulness, from the time I went to work for him until his death–that I regretted what I was doing or where I was at that moment. There was never a time.”

Referring to the Latin meaning of the word for her job, McDonald often reminded people that a secretary was a keeper of secrets.

“[King] could talk to me about anything, possibly things he wouldn’t even burden Coretta with,” she said. “When he was hurting, I was hurting.”

Ms. McDonald rarely saw herself on the front lines of marches, by King’s design.

Ms. McDonald spoke in 2002 about her place on the sidelines during some of the civil rights movement’s key moments.

“I was not in Birmingham the Sunday that Bull Connor brought out the hoses and the dogs, but I wanted so much to go to Birmingham,” she said. King never saw that as her role. “Her role is to take care of my wife and my children when I’m arrested,” she recounted him saying.

On April 4, 1968, Ms. McDonald met Coretta Scott King at the Atlanta airport and told her that her husband had been killed in Memphis, Tenn.

“From that moment on, I didn’t know if I was coming or going,” Ms. McDonald said.

Long after King had died, she couldn’t bring herself to hang photographs of him, rarely worked on April 4, didn’t listen to recordings of him and often refused to reveal anything personal about the man.

“When I am watching television and he is speaking, I quickly turn down the volume and switch stations,” Ms. McDonald wrote in a 17-page autobiographical sketch simply titled, “Dora’s Story.”

“My analyst has assured me that these little quirks of mine are OK, and that the time will come when I can hang Dr. King’s photographs and listen to his voice,” she wrote. “For the time being, this is one of the ways that I cope with his untimely death.”

Ms. McDonald recorded some of her memories in her book “Secretary to a King,” due out in the spring.