From 1956 until his death he was a permanent member of the ensemble at Oper Frankfurt, only interrupted by a short stop at Cologne Opera.
[2] Stern became famous especially for his embodiment of the bass roles in the music dramas of Richard Wagner: Daland in Der Fliegende Holländer, Biterolf in Tannhäuser, Veit Pogner in Die Meistersinger von Nürnberg, King Marke in Tristan und Isolde and Klingsor in Parsifal.
Stern appeared several times at the Salzburg Festival: in 1957/1958 as Bartolo in Le nozze di Figaro, 1958 as Count Dominik in Arabella and in 1964/1965 as Truffaldin in Ariadne auf Naxos.
For Deutsche Grammophon he recorded Biterolf in a complete performance of Tannhäuser and Father Guardian in a section of Verdi's La forza del destino.
In Frankfurt in 1956 he participated as Veit Pogner in a live recording of Wagner's Die Meistersinger von Nürnberg.