Klaus Mertens (born 25 March 1949, in Kleve) is a German bass and bass-baritone singer who is known especially for his interpretation of the complete works of Johann Sebastian Bach for bass voice. Career Klaus Mertens took singing lessons while attending school. He studied music and pedagogy, and had his vocal training with Else Bischof-Bornes and Jakob Stämpfli (song, concert, oratorio) and with Peter Massmann (opera). After graduating with distinction he worked first as a school teacher. In the field of historically informed performance, Klaus Mertens has worked with Frans Brüggen, Philippe Herreweghe, René Jacobs, Sigiswald Kuijken, Gustav Leonhardt and Nikolaus Harnoncourt. With various conductors he recorded the works of Bach, not only the Passions and oratorios, but also – very notably – the cantatas, which number around 200. Mertens took bass solo work in all parts of the project to make the first CD recording of the complete vocal works of J. S. Bach, with the Amsterdam Baroque Orchestra & Choir conducted by Ton Koopman. This project, begun in 1994, took ten years to complete with various soloists in the other vocal parts, and included concert tours in Europe, America and Japan. "In a remarkable display of stamina and consistency, Klaus Mertens sang in every piece that required a bass soloist, 190 in all." He is also involved in the project Dieterich Buxtehude – Opera Omnia of the same ensemble to record the complete works of Dieterich Buxtehude, begun in 2005. As a singer of lieder, he has interpreted songs of Claudio Monteverdi, Antonio Caldara, Wolfgang Amadeus Mozart and Franz Schubert among others. He has performed the title roles of the romantic oratorios Elijah and St. Paul by Mendelssohn and, as music of the 20th century, Paul Hindemith's Requiem and Igor Stravinsky's Oedipus rex. In the classical repertory he has performed with such conductors as Herbert Blomstedt, Roger Norrington, Peter Schreier, Hans Vonk, Christian Zacharias, Edo de Waart and Iván Fischer; and with orchestras including the Berlin Philharmonic, Royal Concertgebouw Orchestra, Rotterdam Philharmonic Orchestra, Leipzig Gewandhaus Orchestra, Dresden Philharmonic, Tonhalle-Orchester Zürich, St. Louis Symphony Orchestra and Chicago Symphony Orchestra. A performance of Gustav Mahler's Kindertotenlieder with the Tokyo Metropolitan Symphony Orchestra under Gary Bertini in 2002 was recorded. In 2005 he performed in the Berliner Philharmonie the Mass in F minor of Anton Bruckner conducted by Kent Nagano. With the Thomanerchor he appeared in the Christmas Oratorio of Bach