Nell Rankin was an American operatic mezzo-soprano. Though a successful opera singer internationally, she spent most of her career at the Metropolitan Opera, where she worked from 1951 to 1976. She was particularly admired for her portrayals of Amneris in Verdi's Aida and the title role in Bizet's Carmen. Opera News said, "Her full, generous tone and bold phrasing, especially in the Italian repertory, were unique among American mezzos of her generation.

Karin Branzell was a Swedish operatic contralto, who had a prominent career at the Metropolitan Opera, New York, and in Europe. Her very wide range enabled her to sing both contralto roles and the occasional soprano role. She was particularly noted for her singing of the music of Richard Wagner, in roles such as Ortrud (Lohengrin), Venus (Tannhäuser), Erda, Brangäne, and Brunnhilde. She was considered on a par with Margarete Klose and Kerstin Thorborg as a Wagnerian contralto. Amneris (Aida), Dalila, Herodias (Salome), and Clytemnestra (Elektra) were among her other renowned roles.