John A. Pople is a theoretical chemist. He is best known for contributing to the development of the Pariser-Parr-Pople (PPP) theory of approximate molecular orbital (MO) calculations on pi electron systems, the methods of Complete Neglect of Differential Overlap (CNDO) and Intermediate Neglect of Differential Overlap (INDO) for approximate MO calculations on three-dimensional molecules, and other developments in computational chemistry.