Rothmüller was an artist of exceptional musical culture. In 1932 Rothmüller made his debut in Hamburg, with the role of Ottokar in "Der Freischütz", and was immediately ranked among the leading European interpreters of heroic baritone rôles. Because of antisemitism in Nazi Germany, Rothmüller returned home to Zagreb in 1933. In 1935 he moved to Zurich, where until 1947 he was a permanent member of the Zurich opera emphasizing the roles in Verdi and Wagner operas. Between 1946 and 1949, he was a member of the Vienna State Opera. In London's Royal Opera House, Rothmüller made his debut in 1939 under the direction of Sir Thomas Beecham. Rothmüller was permanent member of the Royal Opera House from 1948 until 1952. In the Glyndebourne Opera House he performed from 1949 until 1955. Occasionally he also appeared in Edinburgh opera. He appeared on British television in performances of Macbeth and La Forza del Destino. HMV issued a few 78 rpm records on their plum label featuring Rothmüller in rôles from Così fan Tutte, Zauberflöte, Tannhäuser, Rigoletto, Tosca and Andrea Chenier. The Verdi and Puccini performances were much admired in The Record Guide, but the discs were soon deleted and are now very rare. Rothmüller made his debut in United States in 1948, at the New York City Opera. He often performed on the concerts and opera stages across United States. Rothmüller debuted at the Metropolitan Opera, New York City, in 1959 and performed there until 1961, and again in season 1964/65. In 1955 he was appointed as the professor of singing at Indiana University in Bloomington, Indiana. His interest in the Jewish music prompted him to research its history. He arranged the Sephardi folk songs, and in Zagreb in 1932, and Zurich in 1942, Rothmüller founded Omanut, society for the fostering of Jewish music. He was a master of the song interpretation. Rothmüller also wrote a book on the history of Jewish music.
Personal life
Rothmüller was married to Ela with whom he had two sons, Ilan and Daniel. He died in Bloomington Indiana, on 20 January 1993, and was survived by his second wife, Margrit.
Compositions
Three Palestinian folk songs for mixed chorus and piano, Vienna 1931.
Hajimu Nahmanu Bjaliku u spomen for violin, viola and violoncello, Zagreb 1936.
Divertimento for solo trombone, timpani and string orchestra, London 1955.
Mit Shakespeares XXX. Sonett for string quartet, published in: C.T.Frey-Wehrlin, ur., Festschrift zum 60. Geburtstag C.A. Meier 9-13.
