communicator - a person who communicates with others

go-between, intercessor, intermediary, intermediator, mediator - a negotiator who acts as a link between parties

bargainer - negotiator of the terms of a transaction; "he is a hard bargainer"

compromiser - a negotiator willing to compromise; "Henry Clay was known as the Great Compromiser"

holdout - a negotiator who hopes to gain concessions by refusing to come to terms; "their star pitcher was a holdout for six weeks"

negotiatress, negotiatrix - a woman negotiator

representative - a person who represents others

settler - a negotiator who settles disputes