Harkness, also known as A3-21, is Rivet City's security chief in the year 2277.
Harkness is a synthetic humanoid, or "Synth", and is the most advanced android ever created by The Institute, as of 2277. He was created in the year 2242 and worked for the Synth Retention Bureau in the Commonwealth before attempting to escape after sympathizing with the escaped synths he was tasked to capture. The synths working at the Synth Retention Bureau are told that those who try to escape are simply malfunctioning, when in actuality their complex AI has allowed them to start thinking for themselves. The synths that Harkness captured filled his head with ideas about self-determination and freedom, contributing to his decision to escape. “Self determination is NOT a malfunction,” Harkness would say in a holotape before escaping.
He successfully escaped the Commonwealth but was hunted by the Synth Retention Bureau, and had to get surgery to get a new face and voice, as well as having his memory erased, in order to thwart the Bureau and start a new life. After some searching he found Horace Pinkerton, a skilled surgeon that agreed to perform the facial construction surgery and memory swap. After this, he got a job at Rivet City as security chief.
During the day, Harkness will be outside Flak 'N Shrapnel's weapon store in the Rivet City marketplace. He may be on the top floor of the Bridge Tower from midnight to 6:00 a.m. When meeting him for the first time, if you tell him you are going to leave, he'll be stuck at the entrance for the rest of the game. However the Lone Wanderer can still walk past him without incident.
When first arriving at Rivet City Harkness will demand that you state your business in Rivet City before he allows you to enter. With most options you choose he'll let you in. He might say something along the lines of: "Alright you're free to roam around, just don't try anything stupid. Like try to slit my throat when I'm sleeping, you wouldn't try that would you?".
The Replicated Man: Harkness turns out to be the android which Dr. Zimmer is looking for. The Lone Wanderer can make a choice to either help Harkness or Dr. Zimmer who then takes him back to the Commonwealth.
"We've got ourselves a psychopath. Everyone stand clear!"
"You're just pissing me off!"
"You're a petty criminal, but we let you stay here for now."
If you do not return Harkness to Dr. Zimmer, Harkness will stay in Rivet City in a loop, he cannot die. When he loses all his HP he will fall unconscious and revive soon afterwards. Also, if you wait to activate his recall code Harkness will give you a unique plasma rifle: A3-21's plasma rifle, after which you can still turn him in and gain a reward from Dr. Zimmer.
During The Replicated Man quest, after Harkness finds out he is an android and the player is following him downstairs to the Science Lab, he can be pickpocketed for the key to the Ship's Armory.
If the Lone Wanderer allows Zimmer to reclaim Harkness, Zimmer will use a command to restore Harkness to his factory settings.
If you have the Contract Killer perk and kill him through the use of Console Commands, he has 4 ears instead of one.