Peter Gustav Lejeune Dirichlet

Born Johann Peter Gustav Lejeune Dirichlet on 13 February 1805 in Germany, he entered mathematics at a time when many of its core ideas still lacked formal structure. He proved special cases of Fermat's Last Theorem and in doing so created analytic number theory, a field that applies the tools of calculus to questions about whole numbers. He advanced Fourier series, the method of breaking complex waves into simple components, and was among the first to define a function in the precise way now taught in every textbook. His work ranged into mathematical physics—potential theory, boundary-value p…