Sixty years later, Deborah Kerr still gets the glamor, but the singing voice in this iconic clip belongs not to her, but to California born soprano Marni Nixon who died July 24 at the age of 86:
https://www.youtube.com/watch?v=QgVPnWmUqd4
Marni Nixon was heard by more people than any other soprano. She's still being heard today. Somewhere, somebody is watching Natalie Wood in West Side Story, or Audrey Hepburn in My Fair Lady. Those wonderful ladies left a legacy of beauty and class on screen, but it is Marni Nixon who sings Tonight and I Feel Pretty, and especially Eliza Doolittle's I Could Have Danced all Night.
https://www.youtube.com/watch?v=hA9bEKKxTNU
Natalie, Audrey and Deborah wanted to do their own singing in their movies. Audrey Hepburn recorded the soundtrack for My Fair Lady. Other heads, maybe George Cukor's or Jack Warner's, prevailed and Marni Nixon, a loverly looking woman herself sang all the songs that made those shows universally loved.
Marni Nixon didn't sing a lot of easy music. I don't know if fitting yourself into some else's performance via lip syncing is a piece of cake, but I doubt its easier than Schonberg she recorded or Zerbinetta in Strauss's Ariadne auf Naxos she sang to perfection, high Fs and all.
There was the occasional singing-on-screen appearance, notably Sister Sophia (the sweet one) in The Sound of Music. ​Having grown up professionally in Hollywood, she learned to be a quick study, undaunted by difficult scores, demanding vocal ranges or foregin accents.
Later in life Marni Nixon appeared off Broadway in James Joyce's The Dead. Her film career continued off screen and on in Mulan. Her onstage credits went on to include Follies, Cabaret, My Fair Lady (Mrs. Higgins) and Romeo and Juliet. I earn my many years by admitting to loving her performance as Herself in The Mothers in Law with Kaye Ballard and Eve Arden. Marni Nixon does an opera diva send up complete with a horse and a winged helmet.
Marni Nixon was twice nominated for a Grammy Award for recordings of Copland Songs and Schonberg cabaret numbers. Her memoir I Could Have Sung All Night brings back great days of Hollywood, Broadway and opera. Marni Nixon excelled in all three genres. Now she's in heaven, presumably giving voice lessons to Natalie Wood.