According to Mises.org, Carl Menger (1840-1921) "was the true and sole founder of the Austrian school of economics proper." After reading Menger's work, Principles of Economics, Ludwig von Mises decided to become an economist.
Menger is known as one of the three economists (along with Jevons and Walras) who contemporaneously discovered the notion of marginal utility, thus defining many of the concepts that eluded Classical School of Economics (Adam Smith, David Ricardo, etc.) for a century. Menger's ideas founded the Austrian School of Economics - the school of economics that was founded in Austria but is now centered in the US.
The book is a great read and is available to download or purchase from Mises.org.