  During the period 1925–1926 Weyl published a sequence of  groundbreaking papers (Weyl (1925, 1926a,b,c)) in which he presented  a general theory of the representations and invariants of the  classical Lie groups. In these celebrated papers Weyl drew together  I. Schur’s work on invariants and representations of the  \(n\)-dimensional rotation group, and É. Cartan’s work on  semisimple Lie algebras. In doing so, Weyl utilized different fields  of mathematics such as, tensor algebra, invariant theory, Riemann  surfaces and Hilbert’s theory of integral equations. Weyl himself  considered these papers his greatest work in mathematics. 