A casting director is responsible for choosing the few actors who will have the opportunity to audition for the producer and director of the project. They send out a casting call for specific roles in the film, and all the actors respond and submit for those roles. It is the casting director’s job to audition all the actors and narrow it down to a select number of actors that the director and producer will get to see. There may also be smaller less significant roles that a director or producer may not have time to sit through auditions for. In this case, it would be the casting directors job to find the right actor to fill in those roles.
Casting directors of part of the Teamster’s Union, NOT the DGA.