Michael Spivak is the designer of the popular MathTime™ Professional fonts, which he uses to typeset his books on mathematics, and which are marketed by Personal TeX Inc.
He is the author of numerous books (http://www.mathpop.com/mainhtms/bip.htm) on mathematics, including the five-volume Comprehensive Introduction to Differential Geometry (http://www.mathpop.com/bookhtms/dg.htm), Calculus (http://www.mathpop.com/bookhtms/cal.htm), and The Joy of Tex: A Gourmet Guide to Typesetting With the AMS-TeX Macro Package.
He publishes his mathematics books through his company, Publish or Perish Inc. (http://www.mathpop.com) located in Houston, TX.
See also Wikipedia (http://en.wikipedia.org/wiki/Michael_Spivak).