Nell Rankin, who died Thursday at age 81, was a mezzo-soprano who sang in opera houses throughout Europe and the Americas and a stalwart performer at the Metropolitan Opera for over two decades.

She suffered from polycythemia vera, a bone marrow disease, said her husband, Hugh Davidson.

Rankin made her Met debut in 1951, singing Amneris in “Aida,” a role that was to become her trademark there. Other major roles for her at the Met included Marina in “Boris Godunov,” Laura in “La Gioconda,” and Azucena in “Il Trovatore.”

Rankin was born in Montgomery, Ala., in 1926, to a family with musical roots; her great grandfather was reputed to have played in Felix Mendelsohn’s orchestra. Rankin’s vocal skills were recognized early, and as a small girl she occasionally sang on local radio, accompanied by canaries. As a teenager, Rankin undertook more rigorous vocal training, which she financed by teaching swimming lessons. At age 18, at the encouragement of the great accompanyist Coenraad Bos, who had heard her sing, Rankin came to New York City to study music. She and her sister Ruth, who also had ambitions of singing professionally, set up apartment together. Rankin studied with Bos and with the Swedish mezzo-soprano Karin Branzel.

In 1947, Rankin and her sister, a soprano, debuted at Town Hall before an overflow crowd and presented a program of duets and solo operatic numbers. The Times’s critic especially praised her handling of the notoriously difficult aria “O pretres de Baal” from Meyerbeer’s “Le Prophete:” “She sang the difficult, florid music with rich, round tones … set forth cleanly and proved well within the wide range of her voice.” The aria would become her calling card at recitals around the world.

Rankin auditioned at the Met in 1948, and according to her husband was offered a contract by Maestro Max Rudolf, who simultaneously advised her not to take it. Noting her lack of stage experience, he advised her instead to perform in Europe.

Rankin then traveled to Switzerland, where she was quickly hired as the leading mezzo by the Zurich Opera. In 1950, she became the first American to take first prize at the Concours de Musique in Geneva. The next year, La Scala engaged Rankin to be its leading mezzo for the season, and she made her Met debut as well.

In addition to maintaining an active Met schedule – she had 156 performances there in all – Rankin toured extensively in North and South America, where her Carmen was particularly beloved. Among her career highlights were performing “Aida” in Spanish bullrings and a command performance for King Idris in Libya, held in a giant outdoor amphitheater, her husband said.

Saying that she wanted to stop performing before she lost her upper range, Rankin elected to retire in 1976. She taught singers, both privately and for several years at the Academy of Vocal Arts in Philadelphia. She lived quietly with her husband, a medical doctor, also from Montgomery. The two had met when mutual friends back home realized the two – strangers at that point – were both studying in New York.

Many of Rankin’s recordings are still available, including Verdi’s “Requiem” and “Aida,” several Puccini titles, Berlioz’s “Les Troyens,” and Beethoven’s Ninth Symphony, conducted by Bruno Walter.