Tom Mike Apostol (/əˈpɑːsəl/ ə-POSS-əl;[1] August 20, 1923 – May 8, 2016)[2] was an American mathematician and professor at the California Institute of Technology specializing in analytic number theory, best known as the author of widely used mathematical textbooks.

His parents, Emmanouil Apostolopoulos and Efrosini Papathanasopoulos, were Greek immigrants.

producing videos which explore basic topics in high school mathematics.

He helped popularize the visual calculus devised by Mamikon Mnatsakanian with whom he also wrote a number of papers, many of which appeared in the American Mathematical Monthly.

Apostol also provided academic content for an acclaimed video lecture series on introductory physics, The Mechanical Universe.