Ambassador, Legate, Nuncio, Minister, Envoy, Internuncio and Chargé d’affaires all designate a diplomatic agent serving his sovereign or government in a foreign country and are here compared with reference to their order of precedence as fixed by international regulations and protocol.
Ambassador, legate, and nuncio designate a diplomatic agent of the first rank who is accredited to the head of the state in which he serves, is considered to represent both the government and the person of the head of state whom he serves, and as the personal representative of his sovereign or chief executive enjoys certain privileges and precedences not shared by diplomats of lesser rank.
An ambassador (in full ambassador extraordinary and plenipotentiary) is almost always a resident agent, though the term may also denote one who goes on a special mission as the chief executive’s diplomatic agent. In this case he may be distinguished as an ambassador-at-large.
The comparable diplomatic agents of the pope are called legate and nuncio, the difference between them being that a legate goes on a special mission and is clothed with authority to act in the name of the pope and a nuncio serves as the accredited resident ambassador of the Holy See at a foreign court or seat of government.
Minister designates a diplomatic agent of the second or of the third rank. He, too, is accredited to the head of the state to which he is sent but as the representative solely of the government and not of the person of the head of his own state. As an agent of the second rank, he may also be called an envoy, for his full title is envoy extraordinary and minister plenipotentiary.
Internuncio is the designation of the papal diplomatic agent of the second rank equivalent to an envoy extraordinary and minister plenipotentiary. Agents of the third rank, called more fully ministers resident are now uncommon. They perform essentially the same function as the envoy extraordinary and minister plenipotentiary but are usually assigned to less important capitals.
A chargé d’affaires is an agent of the fourth rank who directs diplomatic affairs in place of an ambassador or minister in the absence or lack of such higher-ranked agent. He is accredited to the head of the department dealing with foreign affairs rather than to the head of the state and his appointment may be on a permanent footing and by his home government or on an interim basis by the head of a mission (an ambassador or minister).