An independent person or body officially appointed to settle a dispute:

Arbiter
Mediator
Agent provocateur
Arbitrator

The correct answer is: Arbitrator.

An arbitrator is an independent person or body officially appointed to settle a dispute. The arbitrator’s decision is binding on the parties to the dispute.

A mediator is a neutral person who helps the parties to a dispute to reach a settlement. The mediator does not have the power to make a decision.

An agent provocateur is a person who is secretly employed by a government or other organization to incite people to commit acts of violence or other illegal activities.

Arbitration is a process in which a neutral third party, called an arbitrator, makes a decision about a dispute between two or more parties. Arbitration is a private process, which means that it is not subject to the same rules and procedures as court proceedings. Arbitration is often used to resolve disputes in commercial and employment law.

Mediation is a process in which a neutral third party, called a mediator, helps two or more parties to reach a settlement of a dispute. Mediation is a voluntary process, which means that the parties must agree to participate in mediation. Mediation is often used to resolve disputes in family law, criminal law, and civil law.

An agent provocateur is a person who is secretly employed by a government or other organization to incite people to commit acts of violence or other illegal activities. Agent provocateurs are often used to infiltrate political or social movements and to discredit them.