|Born||25 March 1949|
|Occupation||Classical bass and bass-baritone singer|
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, Saint 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 who had conducted the group in its first performance in 1734. Thomaskantor Georg Christoph Biller directed a recording of Bach's Mass in B minor in 2006. Mertens has also collaborated with the Windsbacher Knabenchor and the Dresdner Kreuzchor performing in the Kreuzkirche as well as in the Frauenkirche. In 2009 he sang the bass part in the St Matthew Passion in St. Martin, Idstein, with Ulrich Cordes as the Evangelist and Andreas Pruys. He performed Bach's cantata Ich will den Kreuzstab gerne tragen, BWV 56, in Wiesbaden and in the Alte Oper Frankfurt, programmed in contrast to Shostakovich's Symphony Babi Jar, conducted by Enoch zu Guttenberg. He performed the Vox Christi, the words of Jesus, and the bass arias in Bach's Johannespassion in a concert on 27 February 2010 in Munich with Mark Padmore (Evangelist and arias), Johannette Zomer, Andreas Scholl, Chor des Bayerischen Rundfunks, Symphonieorchester des Bayerischen Rundfunks, Ton Koopman conducting. He performed the part of Valens in Handel's oratorio Theodora in Eberbach Abbey in 2010. He was bass soloist for two concerts of the Bachchor Mainz reviving church cantatas of Wilhelm Friedemann Bach in June 2010, remembering the composer's birth in 1710.
Mertens has regularly appeared at international music festivals such as the Prague Spring International Music Festival, Maggio Musicale Fiorentino, Festival d'Aix-en-Provence and the Salzburg Festival. In 2006 he sang the bass part of Bach's St Matthew Passion, conducted by Enoch zu Guttenberg, at the Rheingau Musik Festival. With the same ensemble he appeared in 2009 at the 12th Beijing Music Festival in major works of Joseph Haydn, The Creation, the Nelson Mass and The Seasons.
Selected recordings of unusual repertoire:
- Othmar Schoeck: Elegie op. 36, with Mutare Ensemble, Gerhard Müller-Hornbach, NCA, 1993/2008 
- Max Reger: 24 Geistliche Lieder (including 12 sacred songs op. 137), with Martin Haselböck (organ), 2000, NCA 
- Christoph Graupner: 3 Bass-Kantaten with Accademia Daniel, 2002, hr-musik  (in German)
- Georg Philipp Telemann: 47 Generalbass-Lieder, with Ludger Rémy (harpsichord), 2004, jpc 
- Schubert: Winterreise, with Tini Mathot (fortepiano) 2005, Antoine Marchand CC 72152, review Göran Forsling 2006
- Telemann: Cantatas For Bass Voice, with il Gardellino, 2007, ArkivMusic review Brian Robins in Fanfare
- Johann Pachelbel: Arien & Concerti, with Emma Kirkby, Kai Wessel, Jan Kobow, London Baroque, 2007, Cavalli Records CCD 332 review Steven Plank in Opera Today
- Gustav Mahler: Lieder Cycles arranged for Chamber Ensemble, with Mutare Ensemble, Gerhard Müller-Hornbach, NCA 
- Klaus Mertens on bach-cantatas, 2009
- See notes by Archivmusic here.
- Dieterich Buxtehude – Opera Omnia Archived 2010-01-23 at the Wayback Machine
- Kindertotenlieder Archived 2011-07-23 at the Wayback Machine
- Berliner Philharmonie review Alexander Gurdon in Klassic.com (in German)
- Christmas Oratorio[permanent dead link] Konzerthaus Dortmund 2008
- Mass in B minor ArkivMusic
- Klaus Mertens interview Windsbacher Knabenchor, "Süchtig nach diesem Chorgesang" ("Addicted to this choral singing") 2008 (in German)
- Honsack, Daniel (7 April 2009). "Kraftvoll, samtig und zupackend". Wiesbadener Tagblatt (in German). Archived from the original on 9 June 2012. Retrieved 4 November 2010.
- XVIII. Wiesbadener Bachwochen 2009 Archived 2011-07-18 at the Wayback Machine (Bach Weeks)
- Alte Oper 21 February 2010
- Johannespassion on the website of the br choir
- Pfingstkonzerte Archived 2011-07-19 at the Wayback Machine junge kantorei (in German)
- Wilhelm Friedemann Bach (1710-1784) Aufführung wiederentdeckter Kantaten Archived 2011-07-18 at the Wayback Machine (Performance of re-discovered cantatas), Bachchor Mainz, 2010 (in German)
- Bach: Matthäus-Passion Archived 2015-09-23 at the Wayback Machine European Festivals Association, Rheingau Musik Festival, Germany, 2006
- Enoch zu Guttenberg Archived 2009-11-28 at the Wayback Machine concerts 2009
- Dippel, Roland H. (16 June 2019). "Leipziger Bach-Medaille an Klaus Mertens überreicht". Leipziger Volkszeitung (in German). Leipzig. Retrieved 17 June 2019.
- "Klaus Mertens". ClassicsOnline. Archived from the original on February 26, 2012. Retrieved January 3, 2010.
- Tini Mathot on Bach Cantatas Website