Ambassador

You may also be looking for the Ambassador-class starship.

An ambassador is the official diplomatic representative of one government or political entity to another, or to an organization of political entities. Ambassadors also function as the heads of embassies.

Customarily in the United Federation of Planets, ambassadors represent the Federation to non-member worlds, and sometimes member worlds have ambassadors to represent their worlds to the Federation itself.

When protocol does not call for a representative of full ambassador rank, a "liaison officer" drawn from a government's military or civil service corps may instead serve the same duties.