Myths and legends of the USA
First of all, "Forrest Gump" is not just a feature film, it is a myth about America with allegorical characters. After all, in the rich history of our world, all ancient civilizations have their own myths, legends, bylinas, if you will. But America, as a younger, though now so majestic power, does not.
So it creates its own myths in recent history, right here and now, through movies. For example, the Marvel and DC universes are definitely true heroic epics. And Forrest Gump is a nation-building myth, where each character reflects one of the country's key characteristics.