Ambassador Extraordinary and Plenipotentiary. The original idea behind the word "ambassador" is the same as for the German word "Amt", which means "office", not in the
sense of a room but a position of responsibility, a mission. So the first "ambassadors" were messengers carrying messages from one monarch or sovereign (king or queen) to another, and they were
"extraordinary" because they were not ordinary messengers - they got their mission directly from one monarch and had to deliver it directly to another.
The status of Ambassadors was established at the Congress of Vienna in 1815. The main thing was that they were appointed by and officially represent the Head of State
(monarch or president), and they had full powers (pleni + potentiary) to sign international treaties and agreements. In the modern-day world of democracy and mass communications, Ambassadors are
career diplomats working for their governments and promoting the interests of their country abroad.