Cosmic evolution of the relative contribution from stripped stars (dark blue), massive stars (light blue), and AGN (beige) to the budget of H I-ionizing photons (panel a) and He II-ionizing photons (panel b). We label the time of hydrogen and helium reionization and shade the times predicted by our model for the reionization of the Universe. This figure shows the results from our standard model; the trend in massive stars is in part due to the strongly redshift-dependent f_esc (see Table 1).