collaborator

collaborator (http://definr.com/collaborator)

     n 1: someone who assists in a plot [syn: confederate, henchman,
           partner in crime]
     2: someone who collaborates with an enemy occupying force [syn:
         collaborationist, quisling]
     3: an associate who works with others toward a common goal;
        "partners in crime" [syn: cooperator, partner, pardner]