Greek Coin Needs Identified

Hello and welcome.

The coin is not in the name of Alexander himself, but from one of the successor kingdoms. However, for reasons I will elaborate on, I'm fairly sure it's not genuine.

The reverse names the king - in this case, "Basileos Demetriou soteros". Macedonia, Bactria and Seleucia all had kings named "Demetrios"; the one from the Seleucid kingdom known as Demetrios I is the only one who added "Soteros" to his titles on the coins. The "ONP" in the exergue is also indicative of Seleucid coins of this king; it's the date, in Greek numerals (in this case, "159", equal to the year 154 BC. You can find some coins with the same reverses by clicking on the Wildwinds page for this ruler and scrolling down to the coins labelled "Houghton 153" and "154".

Unfortunately, I can't find any indication that coins with this reverse were ever made with the Alexandrian-period "head of Herakles" obverse. By 154 BC, that old "imitation of Alexander" style had long gone out of fashion and this reverse is supposed to be matched to a portrait of Demetrios himself. So, unless you've somehow gotten the pictures mixed up, I suspect that what you have here is a modern "Bulgarian" fake, made from mixed-up dies.