Thebom performed more than 350 times at the Met from 1944 to 1967. She built a second career as a teacher, first at the University of Arkansas, Little Rock, and then in San Francisco.
opera singers to gain international fame and was best known for her Wagner performances, including roles as Brangäne in "Tristan und Isolde" and Fricka in "Die Walküre."
She was born Sept. 19, 1915, to Swedish American parents in Monessen, Pa., and raised in Canton, Ohio. Thebom was discovered while singing in a shipboard lounge as a teenager traveling with her parents to Sweden. An accompanist to famed contralto Marian Anderson heard her.
A New York Times review of a 1944 performance by Thebom at the Metropolitan Opera House as Fricka in Wagner's "Die Walküre" said "her gifts as a vocalist were matched by her histrionic ability in a deeply impressive portrayal."
She also toured throughout Europe and was the first American to perform at Moscow's Bolshoi Opera.
In the 1970s, she became director of the opera program at the University of Arkansas, Little Rock.
"I think it was the fact that there was no program here," she told the Associated Press in 1977. "I could start something that would be a reflection of what I believed was important."
In 1989, she helped establish a training program in San Francisco to nurture the operatic talent of young girls.
"Opera is not for everybody," she told the San Francisco Chronicle in 2001. "It's a highly specific and demanding career that requires an iron will and an incredible amount of mental discipline."
Said Greenberg, "She was very devoted and dedicated to teaching young singers."
Thebom sang in such films as "Irish Eyes Are Smiling” in 1944 and "The Great Caruso" in 1951.
She was divorced and had no immediate survivors.