Oz (originally named Sander) was taken in by Government officials when he was 14 years old. He was told that his parents died in an accidental fire in the factory they worked at, along with a group of their close friends and work colleagues. He was a difficult child growing up and often isolated himself from people his own age to focus on the training given to him by his new parents. Many people tried to break him out of his shell but to no avail, and eventually put his behaviour down to a coping mechanism due to to his parent's deaths and the fact his original Father had been an ex-serviceman and full-time militant who brought Oz up with military discipline. On a physical level Oz was superior to all other Children of Promise and would have been the first to try the new suit had it not been for his unstable mentality and lack of compassion, which made him an unsuitable leader.
After the fall of the first Child of Promise, Olivia, Oz was next in line to try the suit; although by this time he was already in his fourties. When he recieved his suit he dropped his human name, Sander, and gave himself the alias, Oz. He served for several months until his arm was severed by an attacking rebel whilst he was trying to protect the Citadel; the attack tore through his tricep, all the way through his humerus and half way through his bicep. Even with the technology they had, they declared they could put his arm back together but he'd never have full use of it again and would have to retire. With physical prowess being at the forefront of his values, he refused to be shamed by his disability and requested that his arm was fully amputated in order to receive a fully robotic arm. The surgeon did as he requested, but when Oz returned to his Government family things didn't go to plan.
Instead of giving him the arm like he'd predicted, they refused and said spending time working on an arm would be a waste and it'd be more productive to give his place to someone else. Not only that, but they requested he give up his suit so that they could continue improving it for the next Child of Promise. When he refused, his family ordered the guards on duty to seize him and pry the suit from his body: dead or alive. Oz barely escaped from the Citadel with his life. He spent a couple of months in Birminghall finding any information he could about the Government in order to use it in his revenge, this is when he found out about the CoP program and the truth about his parent's murders. He also read up on Olivia and decided that, as one of his own kind who was also used and abandoned by the Government, she would make the perfect partner. He spent the rest of his time collecting high-quality parts which he would later use to construct himself a new arm, and the confidential papers containing the information he needed to do so. When he had everything he needed, he made himself a new arm. Unlike average robotic limbs, Oz fashioned it to make it look thick, human-like and above-all strong to match his personality. Unfortunately, to his dismay, even though his arm looked strong it still wasn't capable of much more than picking objects up and performing limited movement.
Oz left Birminghall and made his way to Milgrief to search for our hero, Olivia.