The pre-eminent Wagnerian soprano of the 1930s and 1940s, she was a Norwegian who achieved stardom quite late in her career at the Metropolitan in New York, doing almost all the Wagner heroines: Sieglinde, Isolde, Brünnhilde, Elsa, Elisabeth, and Kundry. She also sang a lot of these at Covent Garden, and there added to the set with Senta. After the War she resumed these roles, continuing with the same beauty and purity well into her fifties.

Born in Hamar (a little north of Oslo) on 12th July 1895, her parents being singing teacher Marie Flagstad Johnsrud and conductor Michael Flagstad, she went on to study in Oslo and Stockholm. Her debut was in the Oslo National Theatre in 1913, as Nuri in the opera Tiefland by Eugen d'Albert, neither of which I have heard of before. D'Albert was a German of French ancestry who was born in Scotland and died in Latvia, and Tiefland, which premiered in Prague in 1903, was a tale of peasants and loves and betrayals. Nuri was not the lead, anyway. For many years Flagstad remained in obscurity in Scandinavia, doing some opera and some lighter roles. She did a small tour of France in 1921.

Her big break was Isolde in Oslo in 1932, when she was 36 or 37 and considering retirement after an uneventful career. She was invited to Bayreuth, and though in the 1933 season she only sang minor parts, Ortlinde and the Third Norn, 1934 saw her in some of the starring roles of the Ring: Sieglinde and Gutrune.

In that year she auditioned for New York, and her debut there as Sieglinde on 2nd February 1935, nationally broadcast, made her a star. In the same season she did Isolde, Brünnhilde, Elsa (in Lohengrin), Elisabeth (in Tannhäuser), and Kundry (in Parsifal). The only non-Wagnerian role she did in this Met period was Leonora in Fidelio.

Flagstad repeated these triumphs in San Francisco (where she sang their first complete Ring with the other great Wagnerian soprano Lotte Lehmann), in Chicago, and in London. At Covent Garden she did Isolde, Brünnhilde, and Senta in The Flying Dutchman. After the War she returned there and sang in the 1948-1951 seasons. Her final operatic performance on stage was as Dido in Purcell's Dido and Aeneas, and thereafter she confined herself to recitals and recordings.

During the war she returned to occupied Norway because, though politically innocent herself, her husband Henry Johansen was a collaborator with the Nazis: profiteering by supplying them (as well as the Resistance) with goods. He was arrested at the end of the war, died shortly after, and his estate was confiscated.

This soured her relationship with American audiences, though apparently not with the British, because she was at the centre of the Wagner revival at Covent Garden soon after the war ended. In 1950, when Rudolf Bing took over in New York, she was readmitted to the fold; she had already successfully returned to San Francisco. In this period she also performed at many other important venues, including Salzburg, Vienna, La Scala, and Paris.

She directed the Norwegian National Opera between 1958 and 1960, and died in Oslo on 7th December 1962. She graces the current 100 kroner note. Her home at Hamar (Kirkegate 11) is now a museum.

Concise Oxford Dictionary of Opera
http://www.bach-cantatas.com/Bio/Flagstad-Kirsten.htm
http://bassocantante.com/opera/flagstad.html
http://www.jcarreras.homestead.com/Tiefland2.html
toalight for the Kr100 fact

Sound clip of her doing 30 s of Brünnhilde's famous Valkyrie battle cry Hojotoho:
http://www-sul.stanford.edu/depts/ars/sounds/hojotoho.au

One more down in my quest to node the world's great singers.