You searched for: “arbitrator”
arbitrator (s) (noun), arbitrators (pl)
Someone who hears both sides of a dispute and then makes a decision: An arbitrator acts like a judge and determines which side is right.
Both of the authors agreed to accept a decision by an impartial arbitrator as to which book would be published first.
Last year in the case of the divorce, the judge acted as the arbitrator by deciding which parent the children would live with.