Stefan Banach (March 30, 1892 – August 31, 1945) was a Polish mathematician who is generally considered to have been one of the 20th century's most important and influential mathematicians. Banach was the founder of modern functional analysis and a founder of the Lwów School of Mathematics. His major work was the 1932 book, Théorie des opérations linéaires (Theory of Linear Operations), the first monograph on the general theory of functional analysis.