literary agent 
noun
A professional agent who acts on behalf of an author in dealing with publishers and others involved in promoting the author’s work.First there's the author, then the literary agent, publisher, distributor, bookseller and finally the customer....
- The world is lousy with literary agents; and literary agents only get paid when they make a sale; so they're a competitive and fast-acting group.
- The big metropolitan publishers won't look at an author who does not have a literary agent, but a literary agent won't look at an aspiring author who does not have a successful publishing record already.