DJ Tanner (Easter Egg) is a minor boss enemy that you meet during the mission "Freedom of Speech". During this mission, you are sent by C3ns0r807 to deal with the DJ because of his particularly foul language.
The DJ looks rather similar to a Rapscallion type enemy though a bit taller. He's got significantly more health and better weaponry but you otherwise deal with him just as you'd deal with any other Rapscallion. Find cover and shoot from there to take him out easily.