Before Ghost was part of Task Force 434, he was an excellent soldier. We still know almost nothing about him, although he knows many things about the UNSC and even ONI, many things that, in his known time serving with the UNSC, he shouldn't know about. We, at ONI have concluded that he might have been with us before, we still don't know about his life as a civilian, so it is possible that he may have served with us before, although if he did, we're not sure why he would keep his identity a secret. Further analysis and research on him is needed.