Cruel and despicable, even for a Pitt Raider, Mex has been removed from general guard duties by Ashur and sent to guard the gates to Pitt Downtown after bouts of Pitt slave punishment that left many with horrific injuries. Adept with a rifle, Mex is content with tagging escapees, laying down a variety of mines, and watching his prey explode in a variety of impressive arterial spray patterns.
Mex and three of his men keep their guns trained on the road into town all day, ready to blow away any pests or vermin trying to get in.
If you tell him you're a returning escaped slave, he will take all the items in your inventory (except the "hidden weapon" you may have received from Wernher), give you a slave outfit which is automatically equipped (whether you're wearing one already or not), and then tell you to enter Downtown.
If you tell him you came looking for work, he'll invite you to enter through the door to Downtown and fill out an application, whereupon you are ambushed and all your items are taken (except the "hidden weapon" you may have received from Wernher), and you are issued a slave outfit which is automatically equipped.
If you kill him on the way in, you will also be ambushed, with the same result as if you were trying to "apply for a job" (but with different dialogue from the ambushers).