Arch Dornan is a drill sergeant in the Navarro base. Equipped with advanced power armor and a characteristically bad attitude, he is the bane of privates, chastising them for the slightest mishaps and breaches of protocol, especially if he dislikes them. Not much is known about his past life.
Talking to him even while equipped with advanced power armor will end with him forcing the Chosen One to stand guard at the hangar. If dialogue with him is initiated after being sent to guard the hangar, he will react negatively.
Should he spot the Chosen One out of Enclave armor, there is a chance he has them thrown off the base, thinking they are just another civilian. If spotted a second time, he concludes that the Chosen One is actually a spy and raises the alarm. However, with enough points in primary and secondary statistics, one can fool him into believing that they have actually lost their issued set of power armor or were not issued one by sloppy base personnel, resulting in a lengthy tirade and a dismissal to the Quartermaster for another suit.
"Welcome to Camp Navarro. So, you're the new replacement... You are out of uniform, soldier! Where is your power armor? Don't have any? You expect me to believe that, maggot? The truth is you lost an expensive piece of army-issue equipment. That suit is going to come out of your pay, and you will remain in this mans army until you are five hundred and ten years old, which is the number of years it will take for you to pay for a Mark II Powered Combat Armor you have lost! Report to the armory and have a new suit issued to you, then report back to me, private! Dismissed!"
"Soldier, you are still out of uniform. I gave you a direct order to report to supplies and get your issue. Now, get out of my face and don't come back until you look like a soldier! This is the second time you have come to me out of uniform, Soldier. There will not be a third!"
"Trooper, what are you doing here? Get back to your guard post! Mo-ron. If I see you away from your post again, it will be the sorriest day of your short life! You are a danger to us all. That will end now."
Arch Dornan appears only in Fallout 2, however, Cannibal Johnson in Fallout: New Vegas makes a reference to Dornan, remembering him for once catching a private out of uniform and going on the most "ear-blistering rant known to man."