A stuck-up raider with delusions of grandeur, he's vying for Krenshaw's position and has the rifle prowess to back up some of his plans. He knows the history of the place and of Ashur, and he doesn't mind sharing it with you, telling you all about this motley crew.
He can be seen either warming his hands at the fire next to where Phantom, Mona, or Squill are practicing their melee strikes, or shooting at the beer bottles at the same place where O-Dog and Vikia practice.
He will congratulate you for fighting your way out of The Hole, and he will tell you about how most of the raiders were once slaves and also fought their way out of The Pitt, which contradicts the stated fact that there have only been three slaves that have ever done this, these being Gruber, Reddup, and Squill.
Duke informs you that many of The Pitt raiders are actually former slaves who earned their freedom by fighting in the Arena, although most do not like to admit to this fact. The rest are regular raiders from the Capital Wasteland who came to The Pitt in order to join "the biggest gang around." Duke's dialogue suggests that he himself is one such former slave.
Duke refers to the raiders in the Capital Wasteland as "drugged up idiot raiders out in the wild," mentioning how they're an embarrassment and bring shame to the profession.
If he is killed while the player character is wearing Leather Rebel, then you will hear Duke say, "That Preacher lied..."