Intelligence, innovation and integrity-KD Tocher and the dawn of simulation

It is now some 50 years since the advent of discrete-event simulation in the form of the development of the General Simulation Program (GSP) by KD Tocher and his team. The paper considers this innovative step in the context of the earlier history of operational research (OR), simulation and computing hardware and software, for example, being before the emergence of high-level languages. The paper discusses the industrial stimulus for the GSP idea and the pioneering path followed. That GSP work opened the way to a tool that has grown in popularity steadily over time to be now recognized as the most frequently used of the classical OR techniques.