Achilles occupies a central role of importance in the epic poem. Consider the opening lines of the work as evidence of this:
Sing, O Goddess, the Anger of Achilles son of Peleus that brought countless ills upon the Achaeans. Many a brave soul did it send hurrying down to Hades, and many a hero did it yield a prey to dogs and vultures, for so were the counsels of Jove fulfilled from the day on which the son of Atreus, king of men, and great Achilles, first fell out with one another.
It is here that the first inclination of Achilles' importance is evident. Achilles' skill at warfighting allows him to transcend what others can do on the battlefield. Achilles is the embodiment of the Classical warrior, whose arete, or greatness, on the battlefield is the determination for success or failure. He fights for the Greeks against the Trojans and his desire to be regarded as the best to ever take the battlefield. He recognizes that his participation in the war against the Trojans is a way to cement this legacy.