Gwendolyn Killebrew (August 26, 1941[1][a] – December 24, 2021) was an American operatic contralto and mezzo-soprano who worked in Germany and internationally, including the Metropolitan Opera and the Bayreuth Festival.

She was engaged at the Metropolitan Opera (Met) in 1967, and made her debut as Waltraute in Wagner's Die Walküre[1][7] in a new production conducted and directed by Herbert von Karajan, with Birgit Nilsson in the title role, Thomas Stewart as Wotan, Jon Vickers as Siegmund, Gundula Janowitz as Sieglinde, Karl Ridderbusch as Hunding and Christa Ludwig as Fricka.

[8] It was aired live in 1968 as a Saturday afternoon radio broadcast from the Met, in a performance conducted by Berislav Klobučar and with Leonie Rysanek as Sieglinde.

[1] When the new opera house of Kennedy Center in Washington, D.C., was opened on September 10, 1971, she performed in the world premiere of Ginastera's Beatrix Cenci.

[5] She performed in Monteverdi operas, as Ericlea in Il ritorno d'Ulisse in patria in 2003,[11] and as Nutrice in L'incoronazione di Poppea in 2004.

[15] She performed the role of Waldtaube in Schönberg's Gurre-Lieder at the Proms in 1981, with the BBC Symphony Orchestra and choirs conducted by Michael Gielen, and alongside Philip Langridge, John Tomlinson, Günther Reich, Jessye Norman, and Wolfgang Neumann.

A reviewer of a reissue noted in 2003: As Tamerlano, Killebrew has a strong and resonant voice; it rings at the top and has a defined chest voice adding powerful presence to her characterisation – her aria Vuo dar pace in Act I Scene II announces singing of real presence.

Lewis M. Smoley wrote in a book comparing recordings of the Mahler symphonies that she "has a deep, rich, if heavyish, timbre that suits the profound, other-worldly atmosphere of Nietzsche's poetry".