What inspired this armour?

Would it be very glib if I answered that it was probably inspired by the costume design for Lord of the Rings (2001-3)?

Certainly there is nothing in the Greek archaeological or pictorial record that looks anything like what Brad Pitt is wearing here. Arguably, some elements are loosely inspired by actual Greek pieces of armour: the helmet, for instance, looks like a very open-faced and stylised version of the crested Corinthian helmet that was common in Greece from about 650-450 BC. The lines engraved in the corslet may be inspired by the line decoration on some examples of the Greek bell cuirass. But the fact that the corslet is in several pieces, some of which appear to be made of leather, shows that this is just fantasy armour for a fantasy character. His greaves are also of leather, whereas the Greeks always made greaves out of bronze.

In a way it's weird that the costume designers of Troy decided to make his armour so inauthentic, since they seem to have worked much more closely with real historical examples in their design of the armour of ordinary warriors. The troops of Agamemnon are clearly wearing Assyrian-style conical helmets with circular crests; there also seems to be some armour inspired by the famous Mycenaean boar's tusk helmet described by Homer. At least one shield design is clearly taken from the Mycenaean warrior vase while the Trojans use shields and formations inspired by the Sumerian Stele of the Vultures. Of course this is all playing mix-and-match with literally thousands of years of Eastern Mediterranean and Near Eastern military equipment, but at least it has a historical basis somewhere.

For the main characters, however, this all went out the window. None of them are wearing any realistic equipment at all. The only somewhat faithful element of their gear is the fact that it consists mainly of just a cuirass and helmet, without further armour for the arms and legs - but beyond that, it's a free-for-all. Odysseus is dressed like a Roman centurion from a 1950s sword-and-sandal epic. Ajax doesn't seem to be wearing any armour, and his weapon looks like a stone club. Meanwhile, Achilles wears equipment that really owes more to the elves and the Men of Gondor than it does to Greek history. At least his sword seems to be a reasonable approximation of a standard Iron Age European Naue Type 2 sword...