Red supergiants (RSGs) are a He-burning phase in the evolution of moderately massive stars (10-25M⊙). For many years, the assumed physical properties of these stars placed them at odds with the predictions of evolutionary theory. We have recently determined new effective temperatures and luminosities for the RSG populations of galaxies with a factor of ∼8 range in metallicity, including the Mil...

Galaxies in the Local Group span a factor of 15 in metallicity, ranging from the super-solar M31 to the Wolf-Lundmark-Melotte (WLM) galaxy, which is the lowest-metallicity (0.1Z⊙) Local Group galaxy currently forming stars. Studies of massive star populations across this broad range of environments have revealed important metallicitydependent evolutionary trends, allowing us to test the accurac...