Harkness

 is the Rivet City security chief. He is the first person you encounter upon finding Rivet City, and will demand that you state your purpose in Rivet City before he allows you to enter.

Unbeknownst to him, he is really an escaped android from the Commonwealth. In his search for somebody to reconstruct his face and assist him with wiping and replacing his memories, so nobody would recognize and catch him, he ended up in Rivet City where the job was finally done by Pinkerton.

Harkness wears a Rivet City Security Uniform, and wields a Chinese Assault Rifle. He's somewhat tougher than the standard Rivet City Security Guards, being able to survive a couple more hunting rifle headshots than normal.

He is considered a plot-critical NPC, and thus cannot be killed untill the quest "The Replicated Man" is complete. Before that, he can only be knocked out. Harkness seems to remain unkillable even after The Replicated Man is completed, although this may be a bug caused by acquiring both rewards for the quest (by obtaining the rewards from Harkness and Zimmer, then killing Zimmer to prevent him from taking Harkness).

Appearances
Harkness appears only in Fallout 3.

Location
During the day, Harkness can be found outside Flak and Shrapnel's weapon store in the Rivet City marketplace. He can also be located on the top floor of the Bridge Tower from 12:00 Midnight to 6:00AM.

Bugs

 * Harkness may end up permanently stuck in his initial position. This happens if the player either completes the quest Tranquility Lane without going to Rivet City beforehand, or if the player answers "Forget it..." in their initial dialogue with Harkness, when asked why they are in Rivet City. He may still be interacted with if this happens.
 * Harkness can actually be pushed off the deck of Rivet City. When he lands in the water, he is stuck there and never returns to his post, although all the normal dialogue options remain. Moreover, if you speak to Commander Lana Danvers sometime afterwards, she tells the player that she has assumed head of security now that Harkness is gone. This has happened on the PS3 version, after both the Scientific Pursuits and The Replicated Man quests.
 * If you complete the Replicated Man quest by telling him he is an android and letting him kill Dr. Zimmer, he may stand in Rivet City Market permanently in the same spot.

Trivia
Harkness could possibly come from the creators continual references of Doctor Who characters, in this case, Captain Jack Harkness, a time agent from the future who can not die. Furthermore, Captain Jack has had some of his memories removed, rather like Harkness. Could also be from Huckleberry Finn, when the character Ben Harkness is described as "half a man".

Related quests

 * The Replicated Man