* "Aristeia" (ἀριστεία): This term describes a heroic feat or a section of the epic where a hero demonstrates their exceptional skill and prowess. While it doesn't always imply "unstoppability", it often captures the intense and exhilarating moments where a hero shines. Achilles' aristeia in The Iliad is his relentless pursuit and slaying of Hector.
* "Hubris": This term describes excessive pride and arrogance that leads to a hero's downfall. While not directly related to "unstoppable," it often is a factor in a hero's demise. Achilles' hubris in his refusal to rejoin the fight without his armor leads to the tragic death of Patroclus and ultimately his own.
* "Nemesis": This refers to the concept of divine retribution for hubris and other transgressions. It doesn't describe a specific part of an epic, but it highlights the consequences of a hero's unstoppable behavior. The death of Hector, driven by the anger of Achilles and the will of the gods, is a testament to this concept.
Ultimately, the feeling of a hero being unstoppable is created by the narrative itself, the poet's choice of language, and the heroic qualities emphasized. The concept of an "unstoppable hero" isn't necessarily a specific literary element with a definitive term, but rather an effect achieved through various techniques.