BIRGIT NILSSON bestrode the operatic stage as a Wagnerian soprano of unrivalled abilities during the 1960s and 1970s.

Although not confining herself to Wagner — she was also a notable Turandot, Salome, Elektra and Dyer’s Wife (in Die Frau ohne Schatten) in her later years — she will undoubtedly be most vividly remembered by her host of admirers for her portrayals of Brünnhilde and Isolde, roles she sang with extraordinary success in all the world’s leading opera houses.

Her credentials for these roles included a gleaming voice of amazing stamina, a fiery temperament and a not inconsiderable gift as an actress. She always displayed supreme confidence on stage, never seemed to tire and gloried in the sheer strength of her voice, which could pierce through the heaviest orchestral sound with arresting ease.

Well aware of her own worth, she could often be a hard bargainer when it came to fees; quite rightly, she believed that a unique talent deserved an ample reward.

Nilsson came from farming stock and later had a farm of her own, to which she returned gratefully after her exertions in the opera house. She was a born musician, having perfect pitch and playing the piano at a very early age. At 15 she began to sing in her local choir. She then studied at the Royal Academy of Music in Stockholm, where she numbered among her teachers the Scottish tenor, Joseph Hislop.

At first she intended to become a concert singer, but events changed the course of her career, when she made her debut at the Royal Opera, Stockholm, in 1946 as Agathe in Der Freischütz, replacing an ailing colleague. The conductor was Leo Blech, who wasn’t very kind to her, and she even contemplated suicide after the performance.

Fortunately, that unhappy experience was soon put behind her. The following year she came into contact with Fritz Busch (whose son Hans had heard Nilsson singing Lady Macbeth’s sleepwalking scene at the Royal Opera School). He invited her to sing Lady Macbeth in Verdi’s work at the Royal Opera, which proved an immediate success.

Under Busch’s tutelage her career took wing. Indeed, he was instrumental in gaining her first important engagement outside Sweden — as Electra in Idomeneo at Glyndebourne in 1951. Meanwhile, in Stockholm she built up a steady repertoire of roles in the lyric-dramatic field, including Donna Anna, Aïda, Lisa, Tosca, Venus, Sieglinde, Senta and the Marschallin, one of her favourite roles (though she later lamented that nobody ever asked her to undertake it), all sung in Swedish.

Her debut at the Vienna State Opera (where she would be a regular performer for more than 25 years) in 1953 proved a turning point. It was followed by Elsa at the Bayreuth Festival in 1954, then her first Brünnhilde in a complete Ring at the Bavarian State Opera, at the Munich Festival of 1955. After Elsa at Bayreuth, she returned as Sieglinde, Brünnhilde and Isolde in succeeding years, all to universal acclaim.

She first sang at Covent Garden as Brünnhilde in 1957, returning frequently in that role and as Leonore, Elektra and Turandot. Her first appearance at the Metropolitan in New York was as Isolde in 1959, when she was acclaimed, and she sang with that company 184 times, most frequently as Turandot.

Her career was long and distinguished and continued into the 1980s, when she mostly sang Elektra (her last Covent Garden role under Erich Kleiber) and the Dyer’s Wife.

Her voice lost very little of its power or steadiness over the years, and her histrionic ability always improved. Nobody who has seen or indeed heard her as Elektra could doubt her powers as an actress, and her Isolde has had few peers in depicting both the anger and frustration of Act 1, the erotic emotion of Act 2 or the transfiguration of Act 3.

As Brünnhilde, she eagerly conveyed both the human and goddess-like characteristics of the part. A certain unwieldiness marred her performances of Mozart and Verdi, and she was sometimes afflicted by uncertain pitch in this repertory, but in Puccini, in particular as Turandot, she was memorable.

It was not that Nilsson's voice was of such daunting size, as those who sang with her can testify, but it was so unwaveringly produced and so perfectly focused that she had no difficulty filling the largest auditorium or riding the most violent orchestral clamour.

Though a frequent visitor to the Metropolitan Opera, she did not always see eye to eye with its redoubtable general manager, Rudolf Bing, nor with the conductor Herbert von Karajan. This resulted both in her making fewer New York appearances than hoped in the early 1970s and her virtual exclusion from the Salzburg Festival.

Nilsson was on better terms with Georg Solti, and this gave rise to the magnificent recordings by which she will be best remembered, notably the celebrated Decca Ring cycle with the Vienna Philharmonic, Strauss’s Salome and Elektra, and a Turandot for EMI with Corelli and Scotto conducted by Molinari-Pradelli.

Birgit Nilsson, soprano, was born on May 17, 1918. She died on December 25, 2005, aged 87.