Sidney Green was born in an unnamed town in New Jersey. As a child, Green found himself passed between various foster homes and orphanages. Awkward and constantly rejected by his peers, matters were only made worse by a case of chronic bed-wetting. Bullied by fellow children and even adults who were supposed to take care of him, Sidney wallowed in misery until his mutant powers manifested. Large and strong, the bullying--and even the bed-wetting--seemed to taper off. Shortly after his powers emerged, Green joined the Xavier Institute where other teenagers like him trained to become the next generation of mutants. Mentored by the then X-Man Gambit and taking up the codename Onyxx, he would join and train with a squad of other physically mutated, urban teens.