mediator, go-between, intermediator, intermediary

a negotiator who acts as a link between parties

• mediatrix — a woman who is a mediator
• arbiter, arbitrator — someone chosen to judge and decide a disputed issue
• conciliator, make-peace, pacifier, peacemaker, reconciler — someone who tries to bring peace
• diplomat — a person who deals tactfully with others
• harmonizer, harmoniser — a mediator who brings one thing into harmonious agreement with another
• interpreter, translator — someone who mediates between speakers of different languages
• matchmaker, matcher, marriage broker — someone who arranges (or tries to arrange) marriages for others
• moderator — someone who mediates disputes and attempts to avoid violence
• second hand — an intermediate person; used in the phrase"at second hand"

• negotiator, negotiant, treater — someone who negotiates (confers with others in order to reach a settlement)