RV Tauri variables are very luminous stars and are typically given a supergiant spectral luminosity class. However they are relatively low mass objects, not young massive stars. They are thought to be stars that started out similar to the sun and have now evolved to the end of the Asymptotic Giant Branch (AGB). Late AGB stars become increasingly unstable, show large amplitude variations as Mira variables, experience thermal pulses as internal hydrogen and helium shells alternate fusing, and rapidly lose mass. Eventually the hydrogen shell gets too close to the surface and is unable to trigger further pulses from the deeper helium shell, and the hot interior starts to be revealed by the loss of the outer layers. These post-AGB objects start to become hotter, heading towards becoming a white dwarf and possibly a planetary nebula.