Schematic evolution of a massive binary system through the six evolutionary phases considered in this paper: pre-interaction, RLO, stripped envelope star (subdwarf, helium star, or Wolf-Rayet star), compact object, referred to as the compact companion (cc) in a binary system, formation possibly connected with a SN explosion, X-ray silent compact object binary, and HMXB. After the second stage, a fraction of the mass gainers may be fast-rotating and appear as Oe or Be stars, and after NS formation as a OBe X-ray binary. Notably, many systems do not survive the second, fourth, and sixth stage as a binary, i.e. the number of systems evolving from top to bottom is being reduced at these stages. The figure is adapted from Kruckow et al. (2018).