Was Zeus a real person?

I believe there was a theory early on, well before the transliteration of Linear B, that the Greek pantheon originated from deified heroes of the Greek Dark Ages. The "Heroön" of Lefkandi was seen as such a cult place, and after all many of the mythical founders of Greek cities were worshipped in post-Geometric times, e.g. Cecrops in Athens. In a similar vein, it was argued, Zeus and others had been locally worshipped heroes before getting detached from their locality and becoming universal gods. We know today that the Greek gods go back much further in time so the theory doesn't hold water, but at a time the theory might have been seen as somewhat reasonable, especially for materialist historians. A similar phenomenon exists in Scandinavia were there's a tradition according to which the main gods Odin, Freyr and Thor are considered to have been mortal kings of Uppsala (coincidentally the three gods were worshipped there) in some distant past. IIRC Saxo Grammaticus speculates on it, and it might be a thouroughly Christian idea, but at least such thoughts have been voiced before. Finally, the idea that gods were ordinary men propelled by myth and legend to godhood is probably inherently appealing to atheists as it is by far the simplest method to dismiss religions altogether.