Born to Swedish parents who had settled in the USA, Thebom grew up in Canton, Ohio where she sang in the local church choir and participated in a school performance of Martha (Flotow). She also took ballet lessons, which she continued into her forties. To help with family finances she worked as a secretary while continuing to sing at an amateur level.

In 1938 Thebom and her parents travelled by ship to Sweden. During the voyage she was heard singing by Kosti Vehanen, the accompanist and coach of Marian Anderson. Impressed, he arranged for her to receive lessons in New York from Giuseppe Boghetti, who also taught Anderson, and eventually arranged for her to be managed by Sol Hurok, also Anderson’s manager, from 1940. On Boghetti’s death in 1941 she was taught by Margarete Matzenauer and Edyth Walker.

After a recital in Sheboygan, Wisconsin, Thebom’s next engagement a month later was singing Brahms’s Alto Rhapsody with the Philadelphia Orchestra under Eugene Ormandy, in late 1941. During the following years she toured the USA singing in recitals and concerts, and made her New York debut with a recital at the Town Hall in the beginning of 1944, of which the New York Times wrote: ‘Her work revealed a wealth of temperament and an inherent musicianship that presage a brilliant career.’ During the same year she appeared in the film Irish Eyes Are Smiling (she later appeared in The Great Caruso, 1951) and in November made her debut with the Metropolitan Opera on tour in Philadelphia as Brangäne / Tristan und Isolde, followed a few weeks later by her debut as Fricka / Die Walküre at the Metropolitan Opera House itself in New York.

Thebom continued to sing with the Met until 1967, establishing herself as one of the company’s leading dramatic mezzo-sopranos. In the German repertoire her roles included Fricka / Das Rheingold, Waltraute / Götterdämmerung, Venus / Tannhäuser, Ortrud / Lohengrin, Herodias / Salome, Adelaide / Arabella and Magdalene / Die Meistersinger von Nürnberg; in the Italian Amneris / Aida, Laura / La Gioconda, Eboli / Don Carlo, Azucena / Il trovatore and Adalgisa / Norma; and in the French Giulietta / Les Contes d’Hoffmann, Dalila / Samson et Dalila, Carmen / Carmen and Geneviève / Pelléas et Mélisande. She was the first Dorabella in the Met’s popular English-language production by Alfred Lunt of Così fan tutte, first seen at the end of 1951, and made her mark as Prince Orlovsky / Die Fledermaus, Baba the Turk / The Rake’s Progress, Marina / Boris Godunov and The Baroness / Vanessa. She made her farewell appearance as The Countess / The Queen of Spades.

In Europe Thebom’s debut took place in 1950 as Dalila with the Royal Swedish Opera. In the same year she sang Dorabella at Glyndebourne and returned to England in 1952 to record Tristan und Isolde with Furtwängler conducting. In 1957 she sang Dido in the historic production of Les Troyens at the Royal Opera House, London where her extraordinarily long hair was used by the producer Sir John Gielgud to dramatic effect; and also appeared as Carmen at the Bolshoi Theatre, Moscow (the first American artist to perform there) followed by a tour of Russia.

From 1947 Thebom had sung regularly with the San Francisco Opera, where she took the role of Mother Marie in the American premiere of Poulenc’s Dialogues des Carmélites (1957), as well as Cherubino / Le nozze di Figaro, Octavian / Der Rosenkavalier and Orfeo / Orfeo ed Euridice. She also sang Ruggiero to Sutherland’s Alcina with the Dallas Opera in 1960.

After her retirement from the stage in 1967 Thebom continued to give concerts, often in recital with her colleague Eleanor Steber. She was also active as a manager: between 1967 and 1973 she was closely involved in two opera companies in Atlanta, after which she taught voice at the University of Arkansas until 1980 when she moved to the San Francisco State University to head the opera programme there. In the late 1980s she founded the Opera Arts Training Program of the San Francisco Girls Chorus. A board member of the Metropolitan Opera from 1970 to 2008, she chaired the Met’s Pacific Region auditions for fifteen years.

The possessor of a beautiful voice, Thebom cut a glamorous figure on stage. Amongst colleagues she had a reputation as a perfectionist with a strong sense of theatre.

© Naxos Rights International Ltd. — David Patmore (A–Z of Singers, Naxos 8.558097-100).