I don't mean to argue but being the fifth most involved character, his position is kind of vague. He and Foehammer are kind of on the same level, Foehammer you never see but she appears in multiple missions, Johnson plays no direct role to you but is in two cinematics (if you don't count the factual canon of the Legendary ending) and plays alongside you in almost every mission. I don't know what I'd classify them as, whereas Cortana, Keyes, the Monitor, and MC all know and interact with each other, Foehammer and Johnson seem like they're in the immediate background yet I feel like Johnson is more sort of in between that line.