Evidence of African American cultural ingenuity can be found throughout history. This article chronicles the extraordinary story of Leroy Raadel Posey, an African American inventor of a mathematics teaching machine—the Combination Slide Board. Through a historical examination of primary source documents, the man behind the machine is revealed as a mathematics educator whose life’s work focused on providing access to the mysteries behind mathematics. The patent details the purpose of the Combination Slide Board as a teaching machine and calculating device. An examination of Posey’s research and publications exposes his innovations in the emerging field of mathematics education. This analysis reveals the journey of the man, machine, and mathematics (M³) and the creation of the Combination Slide Board as a twentieth-century teaching machine.