According to Luke himself, he can sometimes be overconfident, such as when he underestimated Ares, and was nearly killed. For the sake of resurrecting Kronus, Luke became crueler than ever, and was even willing to send Percy to his certain death into Tartrus through trickery and deceit. Luke proves that he is ultimately good at heart, and chooses to sacrifice himself in order to destroy Kronos once and for all. In this way, Luke is more 'heroic' in the old sense of the terms. (Yes I got this off of wikipedia, don't judge me.) I don't have any specific voice in mind, so, go nuts!