Breuer's year of birth is usually given as 1870, but that's wrong, as evidenced by official documents filled out by his own hand
and now kept at the Vienna Communal Archives (Wiener Stadt- und Landesarchiv) – see below.
Breuer studied voice in Cologne with Benno Stolzenberg, then in Bayreuth with Julius Kniese (and that means: under the aegis of
Cosima Wagner).
He made his debut actually at the Bayreuth Festival in 1894; he was to sing there regularly through 1918. His everyday job was at
the opera in Wrocław/Breslau first (1896/97), in 1900 at the Met, and from the end of 1900 to his death at the Vienna
Court (later: State) Opera.
He hardly ever sang anything but comprimario parts; from the very smallest one-sentence parts up to Steuermann, Melot, David and
Mime in both Rheingold and Siegfried. For his Mimes, which he first sang in Bayreuth in 1896, he was really famous; he sang them
at the Met, in Vienna, in Munich, in Berlin, in Zürich, and again and again in Bayreuth, of course.
From 1919, he was also a stage director both at the Vienna State Opera and at the Salzburg Festival, while continuing also his
tenor comprimario career.

Reference, document source