Marni Nixon, the American cinema’s most unsung singer, died on Sunday in Manhattan. She was 86

She was a classically trained singer and  throughout the 1950s and ’60s she was the unseen — and usually uncredited — singing voice of the stars in a spate of celebrated Hollywood films. She dubbed Deborah Kerr in “The King and I,” Natalie Wood in “West Side Story” and Audrey Hepburn in “My Fair Lady,” among many others.

Her other covert outings included singing for Jeanne Crain in “Cheaper by the Dozen,” Janet Leigh in “Pepe” and Ida Lupino in “Jennifer.” “The ghostess with the mostest,” the newspapers called her, a description that eventually began to rankle.

Before her Hollywood days and long afterward, Ms. Nixon was an acclaimed concert singer, a specialist in contemporary music who appeared as a soloist with the New York Philharmonic; a recitalist at Carnegie, Alice Tully and Town Halls in New York; and a featured singer on one of Leonard Bernstein’s televised young people’s concerts.

Her concerts and her many recordings — including works by Schoenberg, Stravinsky, Webern, Ives, Copland, Gershwin and Kern — drew wide critical praise. Yet as late as 1990, decades after Ms. Nixon had made good on her vow to perform only as herself, she remained, in the words of The Los Angeles Times  “the best known of the ghost singers.”

Ms. Kerr was nominated for an Academy Award in 1956 for her role as Anna in “The King and I” the film’s soundtrack album sold hundreds of thousands of copies. For singing Anna’s part on that album, Ms. Nixon recalled, she received a total of $420.

“You always had to sign a contract that nothing would be revealed,” Ms. Nixon told the ABC News program “Nightline” in 2007. “Twentieth Century Fox, when I did ‘The King and I,’ threatened me.” She continued, “They said, if anybody ever knows that you did any part of the dubbing for Deborah Kerr, we’ll see to it that you don’t work in town again.”

Although the studios seldom accorded Ms. Nixon the screen credit and royalties that she began to demand, both became customary for ghost singers.

The second line of the couplet “But square-cut or pear-shape/These rocks don’t lose their shape,” with its pinpoint high note on “their,” from “Gentlemen Prefer Blondes”? That was Ms. Nixon too. (The film’s star Marilyn Monroe sang most of the rest of the number, “Diamonds Are a Girl’s Best Friend.”)

A petite, fine-boned woman who resembled Julie Andrews, Ms. Nixon was born Margaret Nixon McEathron on Feb. 22, 1930, in Altadena, Calif., near Los Angeles.

She began studying the violin at 4 and throughout her childhood played bit parts — “the freckle-faced brat,” she called her typical role — in a string of Hollywood movies. At 11, already possessed of a fine singing voice, she won a vocal competition at the Los Angeles County Fair and found her true calling. She became a private pupil of Vera Schwarz, a distinguished Austrian soprano who had settled in the United States.

At 17, Ms. Nixon appeared as a vocal soloist with the Los Angeles Philharmonic under Leopold Stokowski, singing in Orff’s “Carmina Burana.” She later studied opera at Tanglewood with Sarah Caldwell and Boris Goldovsky.

Ms. Nixon did occasionally take centre stage, as when she played Eliza Doolittle in a 1964 revival of “My Fair Lady” at City Center in New York. (Ms. Andrews had played the part in the original Broadway production, which opened in 1956.) In 1965, Ms. Nixon was seen on camera in a small role as a singing nun in “The Sound of Music,” starring Ms. Andrews.

On Broadway, Ms. Nixon appeared in the Sigmund Romberg musical “The Girl in Pink Tights” in 1954 and, more recently, in the musical drama “James Joyce’s ‘The Dead’ ” (2000), the 2001 revival of Stephen Sondheim’s “Follies” and the 2003 revival of “Nine.”

Ms. Nixon’s other onscreen credits include “Law & Order: Special Victims Unit.” In the 1970s and ’80s, she was the host of “Boomerang,” a popular children’s television show in Seattle, where she had made her home for some years before moving to Manhattan.

She also supplied the singing voice of Grandmother Fa in Disney’s animated film “Mulan,” released in 1998. (The character’s spoken dialogue was voiced by the actress June Foray.) She taught for many years at the California Institute of the Arts in Valencia, where she was the founding director of the vocal department.

Ms. Nixon, who continued singing until she was in her 80s, eventually came to regard her heard-but-not-seen life with affection. She paid it homage in a one-woman show, “Marni Nixon: The Voice of Hollywood,” with which she toured the country for years.

In the few movie musicals made today, directors tend to cast actors who are trained singers (like Meryl Streep in “Into the Woods”) or those whose star power mitigates the fact that they are not (like Helena Bonham Carter in “Sweeney Todd: The Demon Barber of Fleet Street”).