Playing Blanche DuBois is shattering, say the actresses featured in Nancy Schoenberger’s “Blanche.” But Tennessee Williams’s most indelible character is now a figure of sympathy.BLANCHE: The Life and Times of Tennessee Williams’s Greatest Creation, by Nancy SchoenbergerLast we saw of Blanche DuBois, the brittle antiheroine of Tennessee Williams’s Pulitzer Prize-winning play “A Streetcar Named Desire,” she was being carted off to a state loony bin, uttering her famous line about relying on “the kindness of strangers” that can hardly be improved upon.So when Nancy Schoenberger, a biographer and poet, announced early in her new book, “Blanche,” that she planned to include a few sonnets written from the perspective of DuBois’s ill-fated, unseen young husband, as well as a hypothetical obituary in The Times-Picayune describing how her subject turned her life around after psychiatric treatment, I … yes, blanched.With rare exceptions, such as Jean Rhys’s “Wide Sargasso Sea” (a prequel to “Jane Eyre” that imagines the first Mrs. Rochester), messing with another writer’s characters tends to be tricky business. You have to love, for example, the sardonic headline The New York Times ran when it reviewed Susan Hill’s 1993 novel “Mrs. DeWinter,” a follow-up to Daphne du Maurier’s unimprovable “Rebecca”: “Still Dead After All These Years.”Was “Blanche” going to be a “Still Crazy After All These Years” situation? Or like the goofy-sounding off-off-Broadway attempt at a “Streetcar” sequel in 2006, wherein Blanche and Stella, her sister, were at least in passing represented by throw pillows?Fortunately not. Schoenberger, the author of books on the novelist-socialite Lady Caroline Blackwood and the Johns Wayne and Ford, has now written a lean but graceful character study of DuBois, giving Williams’s most indelible but also frequently misunderstood character her due.It seems incredible now that when “Streetcar” was first staged in 1947, directed by Elia Kazan and starring Jessica Tandy, audiences sympathized with her antagonist and brother-in-law Stanley Kowalski: the brutish factory-parts salesman most remembered for the muscles rippling over his “wife beater” T-shirt and his primordial bellow of “Hey, Stellllla!” (The sympathy was probably in part because young Marlon Brando’s performance was so dazzling.)Even before the #MeToo era, however, Kowalski was being re-evaluated as a domestic abuser, slut shamer and rapist. And as important a proponent of the play as Kazan, who also directed Vivien Leigh in the 1951 film, grew convinced, after his prolonged time with the material, of Blanche’s basic sanity.Schoenberger briefly explains her own fascination with “Streetcar”: Her parents were born in New Orleans, where the play is set, on either side of the Audubon Park Zoo, hearing the roar of the lions there. Her father was an itinerant naval officer — “so handsome in his white uniform!” writes the author, whose enthusiasm sometimes spills over endearingly into exclamation points — but she visited Louisiana often as a child, marveling at the Spanish moss and “dark scurrying cockroaches that seemed to lurk everywhere.” Her mother, a campus beauty queen in Baton Rouge, was an early fan of Williams’s work.If New Orleans and its “miasmal vapors” are pure nostalgia for Schoenberger, for Williams, a gay man who had been mocked as “Miss Nancy” by his cruel father, Cornelius, the sensual city was “liberation,” she notes. He was inspired more tragically by his sister Rose, whose erratic behavior, possibly exacerbated by Cornelius’s violations, led to her institutionalization and then lobotomization at age 26.The dysfunctional Williams family, chronicled extensively in more substantive books like John Lahr’s “Tennessee Williams: Mad Pilgrimage of the Flesh,” moves to the background quite quickly in “Blanche,” though, as readers get acquainted with a series of prominent actresses who have played her, a couple of whom Schoenberger has interviewed, all of whom were haunted by their experience. She also relies heavily, though with a light touch, on previously published material, of which there is no shortage. Talking to a journalist about playing DuBois can resemble a particularly wrenching therapy session.For women and not a few drag queens, Blanche is considered one of the plummest roles in all of show business, though its psychological complexities can prove debilitating. “Like climbing Mount Everest,” NPR called it. (Cate Blanchett, naturally, has scaled Everest twice, playing Blanche both onstage and, in Woody Allen’s “Blue Jasmine,” onscreen, in a modernized version for which she won an Oscar.) Jessica Lange and her partner, Sam Shepard — romantic couples often get oddly enmeshed in the production of “Streetcar” — believed it the equivalent of “Hamlet.” Rosemary Harris: “The loneliest part to live through that I’ve ever played on the stage.” Patricia Clarkson: “It destroys your life when you play that part, you never really recover from it, and everybody who’s ever done it knows.” Jemier Jenkins, one of a few Black women to play her, on the aftermath: “I was very actively trying to release, release, release.”Even the sturdy Ann-Margret found herself “twisted and shaking, confused, agitated, and staring ahead in a daze. I’d lost my grip on reality.” Most starkly Leigh, who turned out to have bipolar disorder, claimed that playing DuBois “tipped me into madness.” “Why has she entered our bloodstream?” wonders Schoenberger, a persuasive proponent of the play’s enduring importance despite its dated elements, most risibly that women hovering around 30 are past their prime. We have lived to see the antiquation of the word “nymphomaniac,” with which the critic Kenneth Tynan dismissed the character, and the reframing of prostitution as “sex work.” (DuBois’s seduction of a 17-year-old male student, regardless, keeps the mantle of moral ambiguity as settled around her shoulders as the “burden” of Belle Reve, the lost family estate, or one of her gossamer scarves.)Talking to Claire Bloom, who played the part on a London stage in 1974, Tennessee Williams once said he imagined Blanche persevering through her time in the asylum and ending up with a flower shop back in New Orleans; in her feminist faux-obit, Schoenberger gives her a co-ownership with Stella, who’s divorced Stanley. It’s a fanciful but satisfying little coda to this project, thankfully confined. (The sonnets, supposedly by Blanche’s doomed young groom, Allan Gray, are gilding the lily.)I’m not sure “Blanche,” which can waft and flit like the butterfly-like creature it chronicles, will satisfy true Williams junkies. But if you’re unfamiliar with this great American classic, or have perhaps let high-school memories of it lapse, this book is a hell of a gateway drug.BLANCHE: The Life and Times of Tennessee Williams’s Greatest Creation | By Nancy Schoenberger | Illustrated | 240 pp. | Harper/HarperCollins Publishers | $30 More