Though some scholars have equated the Mithraic lion-headed figure with Ahriman, Franz Cumont's supposition that it represents Aion-Kronos in Greek (Orphic) or Zurvan akarana in Persian literature is still no doubt sustainable, as well as his theory concerning origin, the diffusion and the syncretic evolution of this deity.But it is true that even Cumont's very persuasive explanation contains several hypotheses, which could be not easily substantiated. I reviewed recent elaboration and supplement of the theory by R. Dussaud and R. Pettazzoni, likewise referring to other opinions. As a result, the crucial position of Asia Minor, given by Cumont to the history of the formation of the Roman Mithraism, seems to be replaced by Syria and Egypt, where Hellenistic cults of Aion-Kronos are comparatively distinctly proved and at the same time Mithraic monuments have been found more frequently than in Asia Minor since the completion of Cumont's Corpus.