a person appointed by a national government to conduct official negotiations and maintain political, economic, and social relations with another country or countries.

a person who is tactful and skillful in managing delicate situations, handling people, etc.

noun

agent , ambassador , attach , cabinet member , charg d’affaires , conciliator , emissary , envoy , expert , go-between , legate , mediator , minister , moderator , negotiator , plenipotentiary , public relations person , representative , tactician , attache , consul , nuncio