Other forms: negotiators
A negotiator is a person who either comes to an agreement with someone else, or one who helps other people reach such an agreement. When two people cannot see eye to eye, it's time to bring in a negotiator.
When two businesses are merging, they can use the help of a negotiator to work out details of the plan. And, when a married couple gets divorced, attorneys or mediators do the work of negotiators, ensuring that the agreement is one that works for each person. Back in the 1500s, negotiator simply meant "businessperson," from the Latin root negotium, "a business or occupation."