Ambassador

An ambassador was the official diplomatic representative of one government or political entity to another, or to an organization of political entities. Ambassadors also functioned as the heads of embassies. Customarily in the United Federation of Planets, ambassadors represented the Federation to non-member worlds, and sometimes member worlds had ambassadors to represent their worlds to the Federation itself. They had the power to file a diplomatic protest. 

As high-ranking official representatives, Federation ambassadors have powers to issue orders and special instructions to Starfleet starship commanders. 

Early in his career, Jean-Luc Picard led an away team to save an ambassador on Milika III. Picard's success gave him great exposure in Starfleet setting the course for his career. 

Picard once called Lwaxana Troi the "acting ambassador of good will" when Doctor Timicin of Kaelon II came aboard the USS Enterprise (NCC-1701-D) in late 2367. Although in that instance, Troi had no official duties on the Enterprise, she did serve as an official ambassador both before and after meeting Timicin. 

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. 

In 2369 Quark told Commander Benjamin Sisko that he was a host, an ambassador of good will, when his bar served as the venue for an official meeting between the Federation and the Wadi.