Stefan Banach

Stefan Banach (March 30, 1892 – August 31, 1945) was a Polish mathematician. He is generally considered to have been one of the 20th century's most important and influential mathematicians. Banach was one of the founders of modern functional analysis and one of the original members 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.

Born in Kraków, Banach enrolled in "Henryk Sienkiewicz Gymnasium" and worked on mathematics problems with his friend Witold Wiłkosz. After graduating in 1910, Banach and Wiłkosz moved to Lwów. However, Banach returned to Kraków during World War I and during this time, he met and befriended Hugo Steinhaus. After Banach solved mathematical problems which Steinhaus considered difficult, he and Steinhaus published their first joint work. Along with several other mathematicians, Banach formed a society for mathematicians in 1919. In 1920, Banach was given an assistantship in Jagiellonian University after Poland regained independence. He soon became a professor at Lwów Polytechnic and a member of the Polish Academy of Learning during this period. Later Banach organized the "Lwów School of Mathematics". He began writing "Théorie des opérations linéaires" around 1929.

On the outbreak of World War II, Lwòw was taken over by the Soviet Union. As a corresponding member of the Academy of Sciences of Ukraine, he promised to learn Ukrainian. In 1941, when Germany took over the city, Banach, his colleagues, and his sons worked as lice feeders at the Typhus Research Institute. When the Soviets recaptured Lwów, Banach reestablished the University. However, because the Soviets were removing Poles from annexed formerly Polish territories, Banach prepared to return to Krakòw. He died in August 1945 after being diagnosed with lung cancer seven months earlier.

Some of the notable mathematical concepts named after Banach include Banach spaces, Banach algebras, the Banach–Tarski paradox, the Hahn–Banach theorem, the Banach–Steinhaus theorem, the Banach-Mazur game, the Banach–Alaoglu theorem and the Banach fixed-point theorem.