Harbinger erst was a innocent child, that lived in the streets of USA, stealing for survive. But, living with no house, he generally mixed up in street fighters, and in a specific fight, he lost his left eye, and he break a bone of the enemy. Habinger, thenceforth, started to break bons for his fun (loving the sound of bones breaking), and became a strong bandit. Curiously, the left eye was lost, like the left horn of his helmet.
As a Saint of Mars
Harbinger meet's Ionia, a gold saint, and because this, wished to be a gold saint for break bones, more and more, and became more powerful than Ionia. He, however, don't served Mars neither faithfully, nor for a good purpose. Habinger was neutral, and only wanted hit, pounch, kick, hurt and pund, follow Mars as a Chaotic Evil Villain and not a Neutral Evil, like Mars.
In Taurus temple, Harbinger after defeats Yuna, Ryuho, Haruto and Souma, teleports them for respectively (Souma with Haruto) the temple of Gemini, Cancer and Leo. After Kouga continues your fight with Harbinger (accustomed with fights), the Taurus saint lets him to pass, for see how much strong Kouga can to be.
After this, Harbinger helps Kiki in the fight with Martians (Mars servants), "betraying" Mars. Later, Harbinger helps to teleport Yuna, Haruto, Souma and Ryuho (again) to the Mars Planet.
Good Bandit, Evil Hero
Habinger never betrayed Mars, because ever was neutral. And continues a neutral hero when Athena recovered the Sanctuary domain, and, for don't lose your patent as a Gold Saint, Habinger served Athena thenceforth, but, still was a neutral guy, and don't loved Athena as his god, fight to break bones, continuing with his goal. Just then, he become a Athena adorer, but recognized he is a imperfect guy (and like to be a imperfect guy) and Athena a perfect godess. But, Athena demonstrated affection for Harbinger, that begin protect her, redeeming himself.