He randomly attack me with the gun runner so I kill them.
I just want to know is he related to any other quest.

One quest. http://fallout.wikia.com/wiki/Isaac_(Gun_Runners)


Dealing with Contreras: Isaac will need the player to bring back 100 pieces of scrap metal in order to manufacture the wares Contreras asks for; this can also be completed by using Speech 80 or Barter 80.