Joe Cobb first makes an appearance very early on, and can be considered as the "dark side" to the tutorial quest in Goodsprings. You find Cobb and Trudy exchanging heated words, and soon learn that Cobb is looking for a man named Ringo, who has taken refuge somewhere in Goodsprings. If you catch up with Cobb before he leaves the tavern, you can learn (by passing a speech check) that Cobb was locked up in the NCR Correctional Facility for crimes of arson, robbery and arson.
Good Versus Evil
Cobb is perhaps a pivotal character for the entire game, as choosing to side with him and help the Powder Gangers take over Goodsprings will make your character inherently evil. It will also cause Goodsprings to have a "Vilified" feeling towards you. On the plus side (if it can be called a plus side) you will gain a higher standing with the Powder Gangers. On the whole it is generally better not to side with Cobb as you will continue to have access to the resources of Goodsprings if you save it. If you are wanting to play through as an evil character however, this is definitely the way to go.