David Kellner (1670, Liebertwolkwitz, near Leipzig – 6 April 1748) was a German composer of the baroque period and a contemporary of Bach.As well as compositions for the lute which are today highly regarded, he wrote on the theory of music, and particularly on writing for equal temperament. His diagram of the circle of fifths is the earliest extant example of the modern layout with major keys and minor keys in two concentric circles, the major immediately outside its relative minor.