Massive stars and supernovae/GRBs are useful future tools for the probe of the
early universe. As the formation of the first and second generations of stars
is supposed to occur in metal-free/poor environements, the standard picture of
massive stars, which is based on the sample in nearby galaxies including our
own, may not be applicable. In this talk, I will address a few issues on the
evolution of massive stars and their consequent explosions in the early
universe. They include the effect of various physical processes (e.g.
rotation, dark matter, pulsation) on the stellar evolution, the possibility of
observing very energetic events like long gamma-ray bursts and some exotic
types of supernovae at high redshift, and massive star populations in the early
universe.