Reddit reviews The Kingdom of the Hittites

The second book of The Iliad mentions allies of Troy coming to swell Priam's ranks, starting on line 816. They list a diverse range of peoples as coming to Troy's aid - mostly other groups from Anatolia, where the Hittites would have ruled at the time, but also people from Scythia, Thrace, Macedonia, and from "far away". Historians debate how much of it is based on history or how much is later insertion, but Hittite sources reveal that Hittite forces fought the Greeks over the area around the same time, so the forces from Anatolia were historical. And the allies close to Troy were likely based on friendly Luwian neighbors. The others are more debatable.

A lost sequel to The Iliad, called The Aethiopis, detailed the arrival of large allied contingents led by Memnon and Penthesilea, intent on relieving Troy before they are defeated by Achilles. We mostly know of it from fragments and retellings, the most complete of which is from Quintus of Smyrna and can be read here.

Memnon was considered to be a historical Egyptian or Nubian king by ancient Western historians, but as history and our knowledge of Egyptian chronology advanced, the consensus became that he does not line up with any known kings. The wiki gives a good overview of his portrayal over time.

If we accept the ~1190-1184 BC dating for the Sack of Troy, then Memnon's expedition falls under either the reigns of Setnakhte or Ramesses III, the first two Pharaohs of the 20th Dynasty of New Kingdom Egypt. They were both known for being warrior kings, sending out military expeditions and driving out invasions of the Sea Peoples (which included Mycenaean Greeks). There's no hard evidence of Memnon's expedition, but putting the Greek account together with our records of these Pharaohs, I've talked to plenty of historians who think that the account of Memnon probably originated from an Egyptian relief force that arrived to oppose the "Sea Peoples".

Penthesilea, on the other hand, doesn't have much evidence. There's just the connection that Ancient Greeks are thought to have based their Amazon myths on encounters with Scythians, and Scythians are mentioned in the list of Trojan allies, so some historians think that Penthesilea and her Amazons might be a mythologized memory of the Scythian forces that came to aid Troy.