Onyx never knew his parents. He knows that his mother was a Tiefling, his father was a human, and they were part of an organization called "The Riftwardens", and that the markings on his body form the Seeker's Sprial, the symbol of their order. He doesn't know anything more about them, his foster father, Damian Duskrunner, tells him that his parents went missing while on a secret mission when Onyx was about a month old. Everybody, Onyx included, believes them to be dead.
Onyx's foster family treated him well, if not strictly, and taught him the ways of Kenabres and the Worldwound. Damian was given orders to scout and patrol the border of the Worldwound, to ensure the Wardstones are doing their job. He took to the duty so well and effectively that they were officially deemed the Duskrunners by the Prelate. An unofficial member since he was a child (only recently made official), Onyx learned to use a bow, hide in the shadows, and take advantage of his gifts from a young age.
"See, but do not be seen. Strike, but do not be struck. Do not risk yourself for pride, our knowledge is worth more than a kill." - Duskrunner's mantra.