Martin is seen to be a lonely servant of his Vault City masters, who is tasked with overseeing Vault 8's inner command center to help ensure that the storage rooms remain undisturbed, and that the doors remain locked. His solitary existence is brightened up with song, though Martin's stutter makes it a particularly difficult thing to listen to.
↑Martin's character description: "{100}{}{You see Martin.}" "{101}{}{You see a slack-jawed man who keeps blinking rapidly.}" "{102}{}{You see Martin.}" "{103}{}{You see a slack-jawed man who keeps blinking rapidly.}" (VCSUPGRD.MSG)