In the early Universe, massive stars played a key role in the early chemical evolution of galaxies and in injecting important amount of ionising radiation in their environments. The first question that will be addressed in this seminar is the following one: can we infer some properties of the first stellar generations in the Universe by studying the surface composition of very metal poor stars in the halo of our Galaxy? The talk will focus on both the regular halo stars and the so-called Carbon Enhanced Metal Poor (CEMP) stars. The second topic that will be addressed in this talk deals with a much more recent event, the birth of the Solar System. Here the question will be: what do the presence of short lived radioactive elements in the proto-solar nebula tell us about the stellar environment of the Sun 4.56 billion years ago? The talk will focus on the discussion of the origin of 26Al and 60Fe in the proto-solar nebula.