  The study of the long-dead early generations of massive stars is crucial in
order to obtain a complete picture of the chemical evolution of the Universe,
hence the origin of the elements. The nature of these stars can be inferred
indirectly by investigating the origin of low-mass metal-poor stars observed in
our Galaxy, some of which are almost as old as the Universe. The peculiar
extremely iron-poor Carbon-Enhanced Metal-Poor (CEMP) stars, whose precise
origin is still debated, are thought to have formed with the material ejected
by only one or very few previous massive stars. The main aim of this thesis is
to explore the physics and the nucleosynthesis of the early generations of
massive stars. It is achieved by combining stellar evolution modeling including
rotation and full nucleosynthesis with observations of CEMP stars.
