Walter Burkert is so struck by the physical resemblance in the traditional representations of the god and the hero—especially by the common feature of their both being unshorn in the manner of a kûros—that he is moved to describe Achilles as a Doppelgänger of Apollo.
Nagy argues that Achilleus and Apollo are formally and thematically mirrored in the dimension of ritual, their structural doubling enacted through shared physical attributes, epithets, and the logic of mênis and loigos.
, The Best of the Achaeans: Concepts of the Hero in Archaic Greek Poetry, 1979thesis