Joseph Louis Lagrange (1775) Developed a general theory of binary quadratic forms to handle the general problem of when an integer is representable by the form ax^2 + by^2 + cxy.
Peter Gustav Lejeune Dirichlet (1837) Pioneering paper in analytic number theory, which introduced Dirichlet characters and their L-functions to establish Dirichlet's theorem on arithmetic progressions [REF].