General terms:
* Representative: This is a broad term for someone who acts on behalf of others.
* Spokesperson: This term implies someone who is specifically authorized to speak on behalf of a group or organization.
* Advocate: This term suggests someone who speaks out in support of a particular cause or group.
* Delegate: This term refers to someone who is chosen to represent a group at a meeting or event.
* Ambassador: This term suggests someone who represents a group or country in a diplomatic capacity.
More specific terms:
* Leader: This term suggests someone who guides and directs a group.
* Mediator: This term refers to someone who facilitates communication and negotiation between two parties.
* Negotiator: This term refers to someone who works to reach an agreement on behalf of a group.
* Lobbyist: This term refers to someone who tries to influence government policy on behalf of a particular group.
* Public relations professional: This term refers to someone who manages the public image of a group or organization.
The best word to use will depend on the specific situation and the role that the person plays.