Morag is the main antagonist in the original NWN campaign. Ten-thousand years before the events of the campaign, Morag was a queen of the Creator Race, a powerful and cruel race of lizardmen from whom the present lizardfolk are descended. At that time, the continent of Faerun was a jungle, but after an ice age dawned upon Faerun, the Creator Race was all but wiped out. In order to sustain themselves, Morag and a handful of her subjects entered an alternate dimension via a magical device known as the Source Stone, which protected them from the cold. Ten millennia later, at the time that the campaign has taken place, the city of Neverwinter has been constructed over the area where the Source Stone lies. Morag desires to regain her power and turn the continent of Faerun into a jungle once more, over which she shall rule as of old. One day Maugrim, who had heard rumors of the Source Stone, encounters it while on a search, and triggers the plague, which is a defense system of the Source Stone. Though infected and dying, Morag uses her power to heal Maugrim and tells him of her ambitions. As she will be able to gain power over from those who die within the vicinity of the Source Stone, she commands Maugrim to spread the plague throughout Neverwinter, which he does. After the execution of Fenthick, Morag begins to appear to Aribeth in her dreams, tempting her to defect to Maugrim's cause as a means of revenge against Neverwinter for seeking Fenthick's death. Aribeth eventually gives in, and agrees to lead a Luskan army in an attack on Neverwinter. Meanwhile, she also has Maugrim and his cult seeking the four Words of Power, ancient Creator artifacts that contain magical power which Morag can use to free herself from the Source Stone.
Source: Wikipedia, "List of Neverwinter Nights characters", available under the CC-BY-SA License.