If your hunting for this fine fellow, he's found by taking the far left door when facing the stairs in the lobby. Through the door you will see a mixture of cubes and soldier type mobs. Through the hidden door are a few more. About 5 total mobs to clear. He's most often found in the corner just as you go through the door from the lobby, by the hidden door, and in the right corner as you exit the hidden door.
Pretty easy kill. Drops a belt of some sort most of the time.