An Ambassador is the official diplomatic representative of one government or political entity to another, or to an organization of political entities Ambassador. Ambassadors are the heads of embassies, or official diplomatic offices of one government established in the capital of another.
Within the United Federation of Planets, ambassadors have one of two known functions. They either represent the Federation and its interests to non-member worlds and organizations as part of the Federation Diplomatic Corps, or they represent their own worlds, which are already members of the Federation, to the UFP itself, particularly on its governing body, the Federation Council.
An ambassador can also be classified as an Ambassador-in-Residence or an Ambassador-at-Large. An ambassador-in-residence is a diplomat who is usually limited to a specific world and/or embassy.
An Ambassador-at-Large, on the other hand, is a diplomat of the highest rank or a minister who is accredited to represent his or her government and is entrusted to operate in several usually neighbouring worlds, or sometimes a seat of interstellar organizations. In some cases an Ambassador-at-Large may even be specifically assigned a role to advise and assist the government in particular issues. Historically, presidents or prime ministers have designated special diplomatic envoys for specific important assignments.
Ambassadors-at-Large has two known ranks: Ambassador and Senior Ambassador. When diplomatic missions that are of great importance and sensitivity requires the collective diplomatic skills and expertise of a team of ambassadors, a Senior Ambassador is usually asked to lead the team in representing the Federation in that mission. These are rare cases.
Senior Ambassadors-at-Large are usually the first choice of their respective governments to move up to the Federation Council and assume the title of Councillor should their government's seat in the Council be made vacant.
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.