Averin Cadash was raised by his mother in Riddleport, where she worked as a cook for the Riddleport Gendarmes, the mercenaries employed by Gaston Cromarcky to keep order and enforce his rule. Averin didn't much care for the lawlessness in town, mainly because he suffered from it. Averin's father had spoken out against Gaston's capricious enforcement of his laws, and was dragged out of his house, never to be seen again for his trouble. Averin's mother went to work for the Gendarmes to secure protection for her and her son. He never tried to stop Cromarcky because his mother's association with the Gendarmes ensured that, while not free from justice, they were at least free from persecution. The second reason was that Averin's mother continually reminded him that as unjust as things might be under Cromarchy, the city had existed in a state of near complete anarchy before he gained power.
When he was old enough, Averin decided to join the Gendarmes, as lawless as they might be, they were still better than piracy. He began training with an old adventurer with a cruel streak: they trained with real swords, and Averin got cut when he did something wrong. Somewhere during his training, he abandoned the sword, deciding a halbert was more to his liking, he kept the sword though, as a backup.
Averin was scrupulously honest in a decidedly unscrupulous group after he was accepted into the Gendarmes. He was resolved to patrol the streets, and keep them as safe as he could, though his comrades grew suspicious over time. They believed that he would turn on them, for whatever reason, Averin never figured out who he was supposed to be intending to sell them out too, but all the same, he was dismissed from the organization. Ironically enough, it wasn't until he was kicked out of the Gendarmes that Averin realized how far gone his hometown was. In that moment he resolved to become a Hellknight, planning to one day bring them to Riddleport, and having justice reign in the pirate town. He knew that he would have to slay a devil in single combat to join the Hellknights, and decided that the Sandpoint Devil would provide adequate practice.
Averin isn't concerned with the politics behind the Order of the Nail, or about Imperial Cheliax and their arrangement with Hell. His only interest is to put an end to savagery in Varisia, whether it is among the barbarian tribes, or in the streets of Riddleport. His worship of Abadar taught him that Asmodeus is no more or less worthy of Veneration than Iomedae, he just isn't overly interested in the trappings of diabolism. He has been known, however, to make the joke that ends with "But in Imperial Cheliax, devils serve you!"