Sarj. Murphy was the head of security in the redoubt.
He despised General Wallace and didn't agree with his policies, nor with the fact that rank was based solely on hereditary instead of on skill and ambition. After the arrival of Ryan's people and their subsequent exile into the outlands, he thought that he had the chance that he needed to take control. But before he was able to, General Wallace sent him and his men out to take out the 'outsiders' ville. They were beaten back by the outsiders, who had been trained by Ryan's people. When he made it back to the redoubt, he staged his revolt. But it didn't last long. General Wallace tracked him down and threw a grenade into the armoury that he was inside, setting off a chain reaction, killing Murphy, and also most likely destroying the redoubt. (Rat King)