Harvey was a trader who came to Nuka-World prior to the Raider invasion that led to the three raider gangs controlling the park. His family was killed, and he was placed in a shock collar amongst many other traders. He considers his fellow captive traders as family.
Harvey is used by raiders stationed at Nuka-World to lure in wasteland survivors, and thus, to a certain death. He pretends to be injured and tells people stumbling across the transit center that he and his wife and son came there to seek shelter.
Random encounter in the Commonwealth, the Sole Survivor can free him after some dialogue.
By passing a persuasion option, Harvey will reveal his true intentions.
By passing a hard persuasion option, he can be offered a stimpak.
He can later be found in Nuka-World, choose to spare or kill him. Harvey has no weapons and will run, and any nearby raiders (and companions) will open fire on him if the Sole Survivor chooses either of the two "dead man" options.
If you choose the conversation option "You're a dead man" when you first run into him again in Nuka-World, everyone attacks him but he never actually dies. He just falls down and gets back up...only to be instantly targeted again.
If Open Season is completed, speaking to Harvey will change his dialogue, as he shows gratitude for your rescue, and is very happy with your decision to aid the traders of the park and totally remove all of the raiders.