In Herodotus histories, in his account of Solons visit to Croesus, he writes, “God is envious of human prosperity... It is Gods way... God tolerates.” Who is this singular god? As far as I’m aware the ancient Greeks were polytheistic, yet this clearly implies monotheism. Is this just a translation thing, or was there a genuine worship of a single god?
The Greek has ὁ θεὸς (Herodotos 1.32.9, e.g.), which is indeed singular, in which case the default is Zeus. Some have tried to connect this singular "god" with the Hebrew God, without convincing results. The evidence is not there. It is just a stylistic choice, and Herodotus here is clearly thinking about the divine force which determines mankind's destiny in all things, appropriately channeling a distinctly "Archaic Greek outlook" at the end of the 5th century in keeping with the writings of Solon, which were extant then and still are, though fragmentary. For discussion on this dubious connection to "God," see Niskanen, The Human and the Divine in History: Herodotus and the Book of Daniel (2004), p.13ff.