Thomas, whose father was of Welsh descent, came from an extremely musical family. After studying psychology at the University of Nebraska however, he worked as a school guidance counsellor before entering Stanford University to study for a master’s degree in child psychology. On learning that the University’s opera department was to mount a production of Falstaff he auditioned and was cast as Fenton. This experience formed his decision to train as a singer; and having studied for three years with Stanford’s professor of singing Otto Schulmann (who had worked as a répétiteur for Karajan at Ulm before World War II) he made his operatic stage debut as the Haushofmeister / Der Rosenkavalier with the San Francisco Opera in 1957, later also singing Malcolm / Macbeth.

After this Thomas moved to Germany, securing a three-year contract with the Karlsruhe Opera from the autumn of 1958. His debut in the title role of Lohengrin was followed by such roles as Tamino / Die Zauberflöte, Alfredo / La traviata, Manrico / Il trovatore, Don José / Carmen, Calaf / Turandot and Lensky / Eugene Onegin. He quickly established himself as a rising star in Germany, making his debut with the Bavarian State Opera, Munich in 1960 as Bacchus / Ariadne auf Naxos; in 1963 he sang the Emperor / Die Frau ohne Schatten at the reopening of Munich’s National Theatre, followed by Walther / Die Meistersinger von Nürnberg two days later.

During 1961 Thomas was cast by Wieland Wagner, with whom he struck up a good relationship, as Radamès / Aida in a new production at the Deutsche Oper, Berlin (conducted by Karl Böhm) and in the title role of Parsifal at the Bayreuth Festival. He was a Bayreuth stalwart during the 1960s, appearing as Parsifal (1961–1963, 1965), Lohengrin / Lohengrin (1962, 1967), Walther (1963, 1969), Tannhäuser / Tannhäuser (1966–1967) and Siegfried / Siegfried and Götterdämmerung (1969, 1976 – the Chereau centenary production). Bayreuth awarded him the Wagner Medal in 1963.

After his success at Bayreuth Thomas made his debut at the Metropolitan Opera, New York in December 1962 as Walther; he sang over one hundred performances with the Met, as Bacchus, Radamès, Florestan / Fidelio and Lensky (all in the 1962–1963 season), followed by Lohengrin (1964), Calaf (1965), Tristan / Tristan und Isolde (1971), the Siegfried Siegfried and Siegmund / Die Walküre (both 1972), the Götterdämmerung Siegfried and Parsifal (both 1974) and Tannhäuser (1979), making his final appearance with the company as Parsifal in 1982. He created the role of Octavius Caesar in Barber’s Antony and Cleopatra in the opening production for the new Metropolitan Opera House at Lincoln Center in 1966 and was told by Franco Zeffirelli, who directed, that he saw Octavius as a member of the Kennedy family.

From 1965, when he sang Bacchus at the Salzburg Festival, Thomas sang regularly with the Vienna State Opera and the San Francisco Opera, notably in the title role of Peter Grimes in 1973. A move into the heavier Wagner roles had been marked by his assumption of Siegmund at the Paris Opera in 1967 and both Siegfrieds at the Salzburg Easter Festival in 1969 and 1970: he recorded the younger Siegfried with Karajan. Also in 1969, he made his debut at the Royal Opera House, London in a new production of Meistersinger and returned in 1971 to sing Tristan in Solti’s memorable farewell production, directed by Peter Hall, with whom he also worked well.

By the mid-1970s the strain of singing both the older Siegfried and Tristan was beginning to take its toll on Thomas’s voice, although in 1974 Harold Schonberg, a tough critic, wrote in the New York Times of his ‘clear, intelligent, smooth singing; sympathetic acting; stylish musicianship’. As late as 1979 he was still singing The Emperor at the Teatro Colón, Buenos Aires; but unfortunately, he died relatively young of a heart attack.

A person of immense intelligence, which informed all his performances, and possessed of an impressive, tall physique, Thomas looked ideal on-stage in his chosen repertoire. He managed to retain the lyrical quality of his voice for much longer than might be expected, given the pressure of singing both Siegfrieds; yet at the same time he was well able to hold his own against singers of the calibre of Birgit Nilsson. His earlier recordings, such as the Lohengrin with Kempe and Bayreuth Parsifal with Knappertsbusch, remain among the finest committed to disc. ‘One must forfeit ego to communicate ideas,’ he said in an interview in 1971. ‘Studying Wagner roles is like peeling an onion. Beneath the first layer is another and another until you reach the centre, then – infinity.’

© Naxos Rights International Ltd. — David Patmore (A–Z of Singers, Naxos 8.558097-100).