Cepheids come in two flavours: type I and type II, corresponding to population I and II stars. Population II stars are the first generation of stars, which formed before the enrichment of the ISM by detritus from earlier stars, and Population I stars like the Sun are the later generation which contain significant amounts of elements other than hydrogen and helium. The name “Cepheid” derives from the fact that the star δ Cephei was the first to be identified (by Goodricke in 1784). Population II Cepheids are sometimes known as W Virginis stars, after their prototype, W Vir, and a W Vir star is typically a factor of 3 fainter than a classical Cepheid of the same period.