A horribly rude and gruff fellow, Metzger runs the DenSlaver's Guild with an iron fist. He demands a lot of respect, but most of it is forced, as he is little more than a crude brute, controlling the Den through fear and intimidation. Rebecca, representing the more honest townsfolk, is not happy with the state of affairs, but is unable to move against him. She openly proposes a handsome reward for the person who kills him.
Seeking more influence, he is investing in several projects he hopes will make a profit for him. He is mainly involved with trying to ascertain the production of jet. He is employing a local gang to guard the raw chemicals needed to produce jet, that he stores in an old church. He is apparently making money off acting as a middle man between Vault City and New Reno for the chemical shipments (both towns have no direct relations).
Vic, the Klamath antiques dealer, tried to swindle Metzger by selling him a broken radio to eavesdrop on transmissions between the Enclave and New Reno. Obviously, the slaver master did not take to this kindly and locked up the trader like a slave, forcing him to repair the radio or rot, whichever came first.
He is the proper person to talk to if you are willing to join the gang, and become one of the slavers. If you are playing an evil character, then this is a very good thing to do. You can go on slave runs, capture slaves, and sell them to Metzger for a lot of money. However, once you've become a slaver, you will get a tattoo identifying you as one. This means that you will lose a chance for getting many sub-quests, since most people will never trust you (and not even want to talk to you), once they see the tattoo and know that you're a slaver; however, being a slaver will earn you respect from the mobs at New Reno.
Killing Metzger is optional, he also has a large number of guards which would need to be dealt with should Metzger be put in danger. Killing Metzger earns 1500 XP, while killing all his men earns 1000 XP. The player can then free the slaves in the back for 1250 XP and report Metzger's death to Rebecca for $1000. Doing all of this naturally earns good Karma as well (+100).