• "Critical Agents" for the story: they are important at a particularly important juncture or for one particularly important thing
  
• Protesilaus: first off the boat at Troy: Thessalian/Aeolian
  
• Philoctetes: his bow is needed to take Troy: Thessalian/Aeolian
  
• Odysseus: stole the Palladion/Palladium* from Troy, came up with the idea for the wooden horse, led the warriors in it.
  
• the Palladion was a statue which was said to be key to Troy's fall.
  
• Sinon: tricked Trojans into opening the gate
• Oilean Ajax: desecrated the sanctuary of Athena: Locrian: close to Thessalian/Aeolian
• INTERESTING THAT NONE OF THESE FIGURE MUCH IN HOMER (except Odysseus and Ajax, but not for stealing the Palladion or for the Trojan Horse or desecrating the sanctuary)
  
• Key "skilled people"
• Machaon (and Podaleirios): doctors, both sons of Asclepius, who is son of Apollo: Thessalian/Aeolian
  
• Nestor: counsellor: Pylos: twin brother of Pelias of Iolcos, who is found in the story of the Golden Fleece and the Argonautica
  
• Calchas: seer
• Others
• Agamemnon: leader
• but he does nothing to really advance the story of the war
  
• Menelaus: the cuckold
• again, it's his wife, but he doesn't do anything that advances the story of the war
• Achilles: the ultimate warrior
• central to Iliad, but the Iliad is just one episode, a kind of glitch, a bump in the road in the overall story of the Trojan War
• Diomedes
• Helps Odysseus steal Palladion
• But overall just a great warrior
• Telamonian Ajax
• Just a great warrior
• A throwback: huge like the warriors of previous times, and has a shield that harks back to the 16th c. BCE, and went out of fashion before where we would place the Trojan War even!
• Supporting roles
• Idomeneus
• Tlepolemos
• Meriones
• etc.

Now, with all that in mind, let's pivot to combine orality and the epic cycle:

A theory about how the Iliad we know came to be.

Dialect Map of Ancient Greek

Fact: the Homeric epics we have are linguistically/dialectically mostly Ionian Greek, not Aeolian. BUT, there are occasional Aeolian forms.

How do we know what is Ionic and what is Aeolian? One good way is from poets, all of whom wrote in the Archaic age but after Homer. Other ways are reports by even later Greeks in various genres. We also have scraps of Mycenaean Linear B from far before when the Homeric epics were written down. We also have inscriptions. So we are in a not-bad position to know a fair bit about dialects in Greek.

Within the epics, we have the characters mentioned above.

So that's the evidence.

Martin West, one of the foremost scholars in this area, postulated (in an article called "The Rise of Greek Epic") that there was an Aeolian/Thessalian epic tradition (see map link above). It arose in Mycenaean times in Mycenaean Aeolia. Why does West postulate that? Because of the many Thessalian heroes who play key roles in the epic story (he's looking at the big picture, not just the Iliad) and also because of the many linguistic forms of words that are best explained as Aeolian in the epics.

West thinks that Ionians (on the map, Ionic also includes Attic, even though it is separated) borrowed the Aeolian tradition and made it their own as much as they could (but some words and characters remained, because they were important or because the words fit the meter really well and no Ionian substitute worked as well). The main tradition of the Iliad and Odyssey  is thus "Ionic," by which is meant that it belongs to Ionia, a name for the Mycenaean and later Greek cities in Ionia as well as across the Aegean on Euboea and in Attica. But it was built from a tradition from Aeolia, and so has remains of that tradition. It's a palimpsest in that it is a story re-written on top of an older version of the same story.

The linguistic evidence and arguments for West's construction rely on extremely technical discussions that only make sense if one knows Ancient Greek. He is very good at that and takes a lot of time on it. Some of that evidence comes from within the Homeric poems, some from slightly later lyric poetry, some from earlier Mycenaean Linea B, etc. You have to know Greek for it to make good sense and to follow it: I don't mean to hide behind that: it's just a fact. Explaining the evidence would be phenomenally tedious and wouldn't help you much, and it would take me a long time to work thru it. You don't need to know the chemistry of baking to bake, or the physics of flight to fly, but they are there and it's important to know that. We can, however, trust West: he's thorough and evidence-based.

You should, in any case, be interested to know the "lay of the land" and that the epic has ancestor roots that reach back far into the regions of Aeolia and Ionia.

Big picture of these eras, partially repetitive of what we've already seen:
Basically, we have Mycenaean times, when a Greek Mycenaean civilization spread all around the Aegean sea. It had writing, and we have Linear B tablets from then, but not a lot, and no really extensive texts at all. The Mycenaean palace culture then collapsed in the late 2nd millennium BCE (around 1250?). Lots of civilizations were lost or set back hard: writing, building large structures, two story building, cities, etc. all ceased. A period of "Dark Ages" began. During the Dark Ages, some of the Mycenaean Greek-speaking cities started flourishing again, while others arose elsewhere. These new cities sent out colonies all over the Mediterranean. So they were "dark" to us, but people lived in them, carried on, built cities, traded, etc. Then writing came back and for us, the lights turned back on: we can start to "see" again when the Homeric texts appear, around 700-900 BCE. Writing and the lyric poets mark the start the Archaic Age.

The epics were forming in Mycenaean times, formed more in Dark Ages, and were in the form we have them by the beginning of the Archaic Age. How do we know that? Because there are things we can reliably date to Mycenaean and Dark Age times in the epics, things that make little sense in the Archaic age (for example, linguistic forms from our texts, types of weapons and objects from archaeology, places and place names from archaeology). And then, in the literature that starts in the Archaic age (lyric poets) and later, the authors know the epics, and they seem to be the epics we have.