The discovery of the tau lepton and the changes in elementary-particle physics in forty years

I describe the discovery of the tau lepton in the 1970s using the SPEAR electron-positron collider and the SLAC-LBL detector of the Stanford Linear Accelerator Center. I also describe the subsequent verification of the existence of the tau lepton and its leptonic nature by experiments at SPEAR and at the DORIS electron-positron collider at DESY As a preliminary to the tau discovery I discuss how I became a physicist and became interested in leptons. This history of the discovery of the tau allows me to give a general picture of the high-energy physics world of forty years ago and to discuss the changes that have occurred in the practice of high-energy physics over these forty years.