Evolutionary tracks in the HRD of the 3 M_⊙ (left column) and 7 M_⊙ (right column) models at five different metallicities (Z = 0 (Pop III, from Murphy et al. 2021, blue), Z = 10⁻⁵ (EMP, this paper, green), Z = 0.0004 (I Zw 18, from Groh et al. 2019, yellow), Z = 0.006 (Large Magellanic Cloud (LMC), from Eggenberger et al. 2021, pink), and Z = 0.014 (solar, from Ekström et al. 2012, purple). Top panel: Non-rotating models (solid lines). Bottom panel: Rotating models (dotted lines).