Karl Gottlieb Bretschneider was a German Protestant scholar and theologian from Gersdorf, Saxony. He is noted for, among other things, having planned and founded the monumental Corpus Reformatorum. He is the father of Carl Anton Bretschneider, a mathematician.
Karl Groos was a German philosopher and psychologist who proposed an evolutionary instrumentalist theory of play. His 1898 book on The Play of Animals suggested that play is a preparation for later life.