A City in Need of Heroes
Waterdeep, also known as the City of Splendors or the Crown of the North, was the most important and influential city in the North and perhaps in all Faerûn. Waterdeep was named for its outstanding natural deep-water harbor, and the city that grew up at this site became the commercial crossroads of the northern Realms. More than 100,000 people made their home in Waterdeep.
Waterdeep was ruled by a council whose membership was largely secret. These hidden Lords of Waterdeep maintained their identities behind magical masks, called Helms, and while they ruled in public, none knew the true identities of most of them. The subject of who the Lords were became a common topic of noble conversation, and some considered it a game to discover the Lords’ identities, a game made more confusing by the fact the Lords themselves set their own rumors afloat.
The Open Lord of Waterdeep is the sole member of the Lords of Waterdeep whose identity is publicly known. There is only one Open Lord at any one time, but when the previous one dies or steps down, he or she is replaced by a new one. Dagult Neverwinter is the current Open Lord of Waterdeep.
Source: Forgotten Realms Wiki