The following article describes the discovery and early marketing history of low-density polyethylene. There are two questions here. Firstly, why was low-density polyethylene discovered at the Max Planck Institute for Coal Research and not, say, at a polymer research institute? And secondly, why was marketing so successful that it earned the Institute and its discoverers about one billion D-marks in license revenues? In financial terms, the discovery of the process for producing low-density polyethylene was the invention of the century. It enabled Karl Ziegler to develop the Coal Research Institute into one of the larger institutes in the Max Planck Society and the only one that financed itself entirely from its own patent and license revenues over several decades. This is a unique story in the history of science.