Moore gave an intensely wrenching performance in Redford's film, "Ordinary People." She played a mother grieving the death of one son, while shutting out the one who lives. It leaves a family crumbling in the process.
It was a side no one had seen before.
While Moore eventually found a lasting marriage in 1983 when she married Dr. Robert Levine, she was rocked by the death of her son Richie who shot himself to death in 1980 in what police ruled was an accidental shooting.
She also revealed in her 1995 biography "After All" that she was a recovering alcoholic.
"It was just a role too, an image of what life should be," she said. "That Mary, sitting by the fireplace, smoking and drinking and laughing. There was a time when the image of a woman who was an alcoholic was... just someone who had really gotten sloppy, gotten dirty."
Nevertheless, Moore went on to star on Broadway and continues to work in film. And a long-awaited Mary and Rhoda reunion happened nine years ago with the two best friends reuniting in their 60s.
After a remarkable career, alongside the obstacles of the disease and personal struggles Moore know has learned lessons, the most important of which is "That's it's OK."
"Whatever it is, it's OK because it's what it is. Don't be looking for perfection. Don't be short-tempered with yourself. And you'll be a whole lot nicer to be around with everyone else," Moore said.