Keith was once a slave of Caesar's Legion until being freed by Captain Parker. Keith has since felt a debt of loyalty to the Captain and has since stayed with him. Currently, Keith has made his home at the Aerotech Office Park where he sells various chems and cheats others at Caravan.
Keith's Caravan Charade: The player has to find evidence of Keith cheating at Caravan. A Barter check of 45 is needed to trick him into telling about his drug dealing and a Speech check of 60 is needed when talking to him to find out how he cheats. Alternatively you can also steal the cards out of the desk in the back right corner of the 200 suite and bring them to Captain Parker as evidence.
After bringing the evidence of Keith's charade to Captain Parker, he will give you the option to assist him in bringing Keith in. Doing so will get you an additional 100 caps.
If the Courier initiates conversation with Captain Parker or Keith while confronting Keith, but just before Parker opens fire, you can glitch him out of shooting at all. He will turn around and walk away, not even finishing the conversation. Talking to Parker about Keith after this will add the quest note to your Pipboy again, as if having the conversation for the first time, but the rest of the quest cannot be repeated.
Additionally, it appears that if you glitch him in this manner, he then allows you to keep passing the Barter and Speech checks infinitely, providing experience each time.