NEW YORK — For much of his career, CNN’s Anderson Cooper rarely talked publicly about being Gloria Vanderbilt’s son.
He wasn’t ashamed. Cooper just didn’t want the baggage, the assumption that his life was set because he was a descendant of Cornelius Vanderbilt, one of the world’s richest business magnates of the 1800s. Since he has the last name of his father, actor Wyatt Cooper, it was easy to keep this quiet.
All of that changes with ‘‘Nothing Left Unsaid,’’ a documentary that premieres Saturday at 9 p.m. on HBO. The film explores Vanderbilt’s life and offers families a blueprint for conversations with aging parents.
Cooper wasn’t as close with his mother as he wanted to be, and when she had a health scare a year ago, realized he didn’t want to be left with questions when she couldn’t answer them.
His mother, now 91, has likely been in the public eye longer than anyone else alive. At age 9, she was on newspaper front pages as the ‘‘poor little rich girl,’’ the subject of a custody battle between her mother and other relatives (her father died when she was 15 months old).
The nickname ‘‘bothered me enormously,’’ Vanderbilt said in an interview. ‘‘I didn’t see any of the press — the newspapers were kept from me. I didn’t know what it meant. I didn’t feel poor and I didn’t feel rich. It really did influence me enormously to make something of my life when I realized what it meant.’’
Money wasn’t an issue; Vanderbilt inherited $4.5 million in 1941. Yet she lived a young life unmoored, with no father and a mother uninterested in child-rearing. She was fascinated with Hollywood, dated Errol Flynn when she was 17 and had a short-lived marriage as a teenager. She married conductor Leopold Stokowski when she was 20 and he was 63. The marriage produced two children and ended when Frank Sinatra began pursuing her.
Vanderbilt later married director Sidney Lumet and then Wyatt Cooper. The Cooper marriage seemed the most grounded, but he died when Anderson was 10.
‘‘She’s the most vulnerable, optimistic person I know,’’ Cooper said. ‘‘She’s the most trusting person. I’m not as trusting as her at all. She’s incredibly optimistic, and I believe the next catastrophe is right around the corner and I want to prepare for it.’’
Cooper looks more like his father and always believed he was most like him. Through the film and its accompanying book, he learned all he had in common with his mother.
Cooper is a gentle guide through the film, going through boxes of memorabilia and drawing stories out of his mother. Much time is spent on the art she has created throughout her life. Her brand of designer jeans — for many people, the thing they most associated with her — gets barely a minute in the nearly two-hour film. Mother and son hope that some people who see the film will be encouraged to speak to elderly relatives about their lives.
‘‘Anderson really knew little about my childhood because I’d never spoken about it,’’ Vanderbilt said. ‘‘So we really got to know each other and became really close in a way that we never had before.’’