HomePeople Biography and filmographyKlaus Mertens Biography unavailable on TMDB. Movies (3)TV shows (0) Movies (3) Wilhelm Friedemann Bach - Cantatas2010 · Self - Bass Ton Koopman plays Bach2004 · Self - Baritone Bach: Christmas Oratorio (Weihnachts-Oratorium)Bach: Christmas Oratorio (Weihnachts-Oratorium)1998 · Self TV shows (0) No credits available.