From A History of Iran: Empire of the Mind, by Michael Axworthy (Basic Books, 2016), Kindle Loc. 662-70:
Who were the Macedonians? Some have speculated that they were not really Greeks, but more closely related to the Thracians. Or perhaps they descended from some other Balkan people influenced by the arrival of Indo-European Greeks. They had come under heavy Greek influence by the time of Philip and Alexander—but even at that late stage the Macedonians made a strong distinction between themselves and the Greek hangers-on who accompanied Alexander’s eastern adventure. In the fifth century BC, Macedonians were normally, like other non-Greeks, excluded from the Olympic games. But the Persians seem to have referred to them as “Greeks with hats” (they were known for their wide-brimmed hats), and Herodotus too seems to have accepted them as of Greek origin. Like the Medes and Persians in the time of Cyrus, as well as many other militant peoples from mountainous or marginal areas, the Macedonians had a strong sense of their collective superiority—but they also sustained many private feuds among themselves. They were notoriously difficult to manage.