Population III stars are the first generation of stars formed in the universe, primarily composed of hydrogen and helium. They emerged after the Big Bang when the universe was still young and lacked heavier elements. These stars are believed to have been massive, burning brightly and quickly, and they played a crucial role in the evolution of the cosmos. As Population III stars aged and died, they exploded in supernovae, creating and dispersing heavier elements into the surrounding space. This process contributed to the formation of Population II stars, which contain more complex elements, and ultimately led to the development of galaxies and planetary systems.