Jackson Mason

Jackson Mason is a character of the beyond the blue series. He was in the military camp where the group originally came from and stays there since. When the group made it back, he was still there following orders
Jackson is way older than the comander and hates taking orders from him. He plots a coup against him and wishes to overthrow him and take his place instead. They don't make it though, as William makes his move first. Jackson then frees the commander and asks for his help against William. The coomander helps him but Jackson plans to kill him because he wants to be in charge. They have a  talk in the cell but the commander is saved in the end. Jackson escapes and William releases the commander as this is a democracy from now on.
The group under Jackson's command meet up and regroup, and decide they want to rule the military base instead of run away, because back there there are supplies and women, which don't exist outside the walls.
Moving underground, they contact some of the men in the camp and take them on their side. Inside the camp, there are clearly two groups, one is William's people, and the second is the commander's. Some more level headed people (commander's right hand, James Davis etc) are in between, trying to bridge the gap between these two. Suddenly, the soldiers that are in the base are threatened by Jackson's men. Jackson takes lead and disarms all soldiers by threatening innocents. He has the commander and William beaten up, and has both their hands broken. For the next months, both of them are unable to do simple tasks. William's left hand is permanently damaged and does not fully heal. 
After a few months pass, the two decide to work together and bring Jackson down. After  beating some of his men, they take their weapons and head to the lockers. They successfully open them up and give some soldiers weapons. Jackson then appears and says those weapons are empty, and that he keeps the bullets away, just to be sure. Then a slaughter ensues, and many are killed. However, William has sent another party (the civilians from his group) to another location, where they find some weapons and attack jackson's forces from behind. Jackson's forces fall back and escape the base, never to be seen again.
The ones left behind are executed due to committing treason