Trojan War
The Trojan War is another legendary event that was certainly based on something real. We know Troy was a real city that was actually razed around 1190 BC, and we have a lot of evidence that says the Mycenaean Greeks and the Hittite Empire fought several conflicts over the city (which was a powerful city-state and vassal of the Hittites at the time). The Trojan War from The Iliad is either a legendary account of the most glorious Mycenaean victory in these wars or perhaps a dramatization of the entire series of wars distilled into one mythical conflict.
As for the people mentioned in the stories, though? No telling. Many were likely based on actual nobles from the conflicts, but Greek mythos has a habit of adding later heroes to famous stories. Combined with the massive time gap before we inherit our earliest surviving copy of the story, at least some of the characters were probably added later. Serious scholarship tries to identify which parts of The Iliad are most guilty of this and which parts most resemble its Bronze Age origins.