A master trader and barterer, Jack is a jovial sort, and not just because he's set up shop next to the raider strip club. He mends the raider's equipment, which keeps him busy and unable to continue modifications on his pride and joy: The Terrible Shotgun that he whips out for a little fun.
Despite being a raider, Smiling Jack is not aggressive to the player (unless provoked). This is because as a trader, he doesn't care who buys or sells from his store, so long as the caps are there. He holds no loyalty to the raiders he lives with, as he does not turn aggressive even if the player kills them in his sight. Still, he urges the player not to let them see him trading with an outsider, likely fearing that the raiders would turn on him if they were caught.