Christian Gustav Adolph Mayer (15 February 1839 – 11 April 1908) was a German mathematician. Mayer was born on February 15, 1839 in Leipzig, Germany. His father was a businessman from Leipzig. He studied at the University of Leipzig, University of Göttingen, University of Heidelberg and University of Königsberg. He completed his doctorate from the University of Heidelberg in 1861. Several letters were exchanged between Mayer and mathematician Felix Klein from 1871 to 1907. Those letters provide insights into the scientific and personal relations among Felix Klein, Mayer and Lie over the period.