Sometimes Anderson Cooper imagines himself as the Thomas Cromwell to his mother’s Henry VIII, the voice of reason — the tether — to her buoyant impulsiveness. And sometimes he pictures Gloria Vanderbilt, who has been in the public eye since her birth 92 years ago, as an emissary from a distant star, marooned on this planet and trying to make sense of it all.

“I always viewed my role as helping her navigate this time and place,” Mr. Cooper said recently. But in the documentary of her life, “Nothing Left Unsaid,” airing on HBO on April 9, with Mr. Cooper as his mother’s interlocutor, and in the epistolary memoir the two have made together, “The Rainbow Comes and Goes: A Mother and Son on Life, Love, and Loss,” out Tuesday from Harper, what instead unfurls is the ways in which this family of two has survived unthinkable losses. There was the death of his father when Mr. Cooper was just 10, and the suicide of his brother, Carter, at 23, a decade later, as Ms. Vanderbilt watched her son’s hands slip from the terrace of their apartment on Gracie Square.

In that same decade, Ms. Vanderbilt would make a fortune to rival that of her forebear, Cornelius Vanderbilt, from bluejeans emblazoned with her name, and then lose it all when her psychiatrist and lawyer colluded to defraud her of her many lucrative licenses. (It was Bill Blass who came to the rescue, writing her a check for a quarter of a million dollars.) And yet, Mr. Cooper said, “She has this enduring optimism and this sense that the next great love or the next great adventure is just around the corner, and she’s about to embark on it.”

The other day, Ms. Vanderbilt brandished her familiar u-shaped grin and her Old World accent, padding about her jewel-box Beekman Place apartment in bare feet. (Later, she would slip on a pair of gold sneakers to give a tour of her artist’s studio one floor below.) “The phone can ring, and your life can change in a blink,” she said, emphasizing that last word and concurring with her son’s assessment of her nature.

“I also believe you sort of attract what you want, what you’re looking for, and I think that one must always be in love. To be in love with a person is of course ideal, but you can be in love with a flower, a tree, an idea. Just waking up in the morning, you know. It’s an attitude, an attitude of romantic readiness,” she concluded firmly, quoting F. Scott Fitzgerald. “We have to have that.”

Ms. Vanderbilt, whose father died when she was 15 months old, has been making headlines since her birth. In 1934, the tabloids called her “The Poor Little Rich Girl.” That was the year of the bitter custody battle between her aunt, Gertrude Whitney, and her beautiful, too young, hapless mother, Gloria Morgan Vanderbilt, who loved parties and the allowance that accrued to her from her daughter’s trust fund. She made headlines, too, for her storied romances — to Howard Hughes and Frank Sinatra, among many others — and her four marriages, the first, when she was just 17, to an abusive Hollywood agent rumored to have murdered his first wife.

Ms. Vanderbilt largely raised herself, a kind of emotional orphan careening from marriage to marriage before finding happiness with Wyatt Cooper, Mr. Cooper’s father, a screenwriter and actor from Mississippi.

“Wait a minute,” Mr. Cooper writes in “The Rainbow Comes and Goes” of his mother’s first marriage. “You started dating a guy who was a gambler and rumored to have killed someone? That’s not usually the kind of information put in their Tinder bio to attract dates. Didn’t you think that was somebody you should probably stay away from?”

Recalling that exchange, Ms. Vanderbilt said: “Of course, you always think you can fix things. You always think you’re the one who can.”

Ms. Vanderbilt has been hashing out her story in all mediums for most of her life. In her glittering collages, faux naïf paintings and her signature “dream boxes,” there are fatherless figures, distant mothers and recurring images of Ms. Vanderbilt’s beloved nanny, Dodo, who gave her the love and constancy she craved. In many of her eight books, a body of work that includes four memoirs, a book of poetry and an erotic novel, published when she was 85 (and which Mr. Cooper, stretching the limits of filial devotion, read in galleys), she continued that interrogation.

Of the erotic novel, “Obsession,” she said: “That was so much fun. It was almost as if somebody else wrote it and it just sort of fell on the page. When I recorded the audiobook, though, I thought: ‘What have I done? Poor Anderson!’”

Clearly, Mr. Cooper’s inheritance from his mother isn’t tragedy and it isn’t money, as he and his brother were taught at a young age there was no pot of gold for them — though he and she share the same steely work ethic — it’s resilience, made springier by a sense of humor.

Both the documentary, directed by Liz Garbus, and the memoir, which is a series of emails between mother and son, have Mr. Cooper investigating the emotional landscape of his mother’s life, and in so doing examining his own.

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They were a year into the documentary when Ms. Vanderbilt fell ill with a serious respiratory infection. She didn’t tell her son just how serious it was, and he left town on an assignment, never learning until his return that she’d been hospitalized. He was deeply rattled, and rued his reflexive impulse to put his work first and view any intrusion as an inconvenience.

On her 91st birthday, they began “a new kind of conversation,” as he writes, by email, which Ms. Vanderbilt takes up with characteristic enthusiasm. It is a remarkably frank and tender undertaking. In one exchange, Ms. Vanderbilt recalled her son coming out to her when he was 21, and being stricken with guilt about a derogatory comment she’d once made, that she would feel she had failed as a parent if her child was gay. As it happened, Mr. Cooper had no memory of the incident; instead, he recalled only the positive way she’d described a gay couple when he was growing up. “I rejoice that you’re gay,” she writes her son.

“She rejoices in everything I do,” Mr. Cooper said. “I was talking to Andy Cohen” — the TV and radio host — “and his mother is a tougher critic. She’ll say to him, ‘Hmm, not your best show.’ But my mom is very much a cheering section. I can do no wrong. It’s always been that way. If I told her I wanted to dye my hair blue, she’d be happy. You couldn’t rebel against her. There is nothing you could do that a) she hadn’t already done, and b) she wouldn’t be fine with.”

Both Mr. Cooper and Ms. Vanderbilt impose order on their lives through their work. Ms. Vanderbilt’s environments have long been as much a canvas as her actual paintings. “It was interesting to hear her talk about it,” Mr. Cooper said. “To hear her cop to it. If only you can change the color of the walls, everything will be O.K. But once that’s done, it feels O.K. for a day or a week, and then she realizes the carpet needs to be redone or she has to move.”

Decorating is autobiography, Ms. Vanderbilt likes to say. “Of course, everything is autobiography,” she added. Throughout the decades, Ms. Vanderbilt’s fantastical interiors — rooms layered from floor to ceiling in gingham or antique quilts — settings as intricate as her artwork, have showed up in Vogue, House & Garden, W, Life and Vanity Fair.

The Beekman Place apartment is like something out of “The Arabian Nights.” Its walls are painted in shades of pink, trimmed with glossy black. There are Russian icons, swoops of fabric, Ms. Vanderbilt’s idiosyncratic and lovely artwork and many portraits of Ms. Vanderbilt and her family.

You can count the Ninas in cartoons of Ms. Vanderbilt by Al Hirschfeld. There’s a full-length Sargent-style painting of Ms. Vanderbilt by Aaron Shikler, and another of her mother painted the year before Ms. Vanderbilt’s birth, looking pensive and sad. There are photographs of Carter and Anderson by Diane Arbus. “I’ve been told by critics that my photograph resembles a Roman death mask,” Mr. Cooper said of his baby photo. It does.

The innards of an antique desk are painted in red and white stripes, a backdrop for a dancing antique figure and a glittery peacock. In her bedroom, an enormous quartz crystal sits like a baby meteor in the fireplace, the mantel of which Ms. Vanderbilt has painted with stars and emblems and mottos, like one paraphrasing Albert Einstein: “The distance between past, present and future is only an illusion, however persistent.”

“It’s one of the great wonderlands,” Wendy Goodman, design editor of New York magazine, said of the apartment. Ms. Goodman collected many of Ms. Vanderbilt’s interiors in her 2010 book, “The World of Gloria Vanderbilt.” “It’s a constant laboratory for her. She’s always repainting and redecorating. It’s like a tonic for her.”

Ms. Vanderbilt’s enthusiasms can sometimes run amok, said her son, recalling dinner parties that grew from a few guests to more than 30, and shifting from her apartment to his at the last minute. “Things can snowball,” he said. “Or she won’t show up.” There was the year he and a partner were spending Thanksgiving on Long Island, and his mother promised to come and bring the bird. On the day, her car arrived without her, though she had a sent the turkey. “It was precooked,” Mr. Cooper said, “which I appreciated.”

Mr. Cooper’s own nature is signified by a profound wariness and a strong belief that disaster is always around the corner. He sees himself not just as a realist, but as a catastrophist. “I always wanted there to be a plan,” he said. “And with my mother, there wasn’t one. It’s why I needed to get a job as soon as possible.” (Mr. Cooper has been working since his father’s death, when he became a child model, not because he yearned to be in front of a camera, but because modeling was a profession that offered a substantial paycheck to underage laborers.)

Mr. Cooper described a trip to Studio 54 when Ms. Vanderbilt was again dating Sidney Lumet (who had also been — stay with me here — husband No. 3) after Mr. Cooper’s father’s death. The event was a premiere for Mr. Lumet’s movie “The Wiz,” and Mr. Cooper, who was 10 at the time, recalled riding in a limousine with Michael Jackson. “I remember people chasing the car, which I thought was kind of funny,” he said. “I remember watching him dance, and I actually remember turning to someone — this is going to sound insane — and saying: ‘He’s really good at this. He should pursue it.’ I was always concerned about people’s financial viability and career choices. I would always ask people how they could support themselves.”

Mother and son concluded their emails to each other just before Ms. Vanderbilt’s 92nd birthday in February. Mr. Cooper asks how she’s feeling about death, while noting that her funeral plans have always been very detailed. Ms. Vanderbilt does share a few of her instructions: If in a church, how about St. James’? If an open coffin, she’d like to be dressed in a Fortuny gown; Mr. Cooper can pick the color, and they are in the cedar closet in her apartment. Do not have the funeral cosmeticians do her face. Please ask Judy Collins to sing “Amazing Grace.”

And as is her way, she cheers for her son, exhorting him to put aside his pessimism. “Excelsior!” she writes. For her part, Ms. Vanderbilt is sanguine about her own mortality. She quotes Woody Allen, who was once asked whether he’d like to live on in the hearts of people after his death and replied, “I would prefer to live on in my apartment.”